U.S. patent application number 12/369067 was filed with the patent office on 2009-08-13 for image processing method and image processing apparatus.
This patent application is currently assigned to RICOH COMPANY, LTD.. Invention is credited to Yoshihiko Hotta, Tomomi Ishimi, Shinya Kawahara.
Application Number | 20090203521 12/369067 |
Document ID | / |
Family ID | 40810660 |
Filed Date | 2009-08-13 |
United States Patent
Application |
20090203521 |
Kind Code |
A1 |
Ishimi; Tomomi ; et
al. |
August 13, 2009 |
IMAGE PROCESSING METHOD AND IMAGE PROCESSING APPARATUS
Abstract
To provide an image processing method including at least one of
recording an image onto a thermoreversible recording medium in
which transparency or color tone reversibly changes depending upon
temperature, by applying a laser beam with the use of a
semiconductor laser device so as to heat the thermoreversible
recording medium, and erasing an image recorded on the
thermoreversible recording medium, by heating the thermoreversible
recording medium, wherein an intensity distribution of the laser
beam applied in the image recording step satisfies the relationship
represented by Expression 1 shown below,
1.20.ltoreq.I.sub.1/I.sub.2.ltoreq.1.29 Expression 1 where I.sub.1
denotes an irradiation intensity of the applied laser beam in a
central position of the applied laser beam, and I.sub.2 denotes an
irradiation intensity of the applied laser beam on a plane
corresponding to 95% of the total irradiation energy of the applied
laser beam.
Inventors: |
Ishimi; Tomomi; (Numazu-shi,
JP) ; Kawahara; Shinya; (Numazu-shi, JP) ;
Hotta; Yoshihiko; (Mishima-shi, JP) |
Correspondence
Address: |
COOPER & DUNHAM, LLP
30 Rockefeller Plaza, 20th Floor
NEW YORK
NY
10112
US
|
Assignee: |
RICOH COMPANY, LTD.
TOKYO
JP
|
Family ID: |
40810660 |
Appl. No.: |
12/369067 |
Filed: |
February 11, 2009 |
Current U.S.
Class: |
503/201 |
Current CPC
Class: |
B41J 2/4753 20130101;
B41M 5/3335 20130101; B41J 2/442 20130101; B41M 5/323 20130101;
B41M 2205/04 20130101; B41M 5/305 20130101; Y10S 430/146 20130101;
B41J 2/45 20130101 |
Class at
Publication: |
503/201 |
International
Class: |
B41M 5/26 20060101
B41M005/26 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 2008 |
JP |
2008-032155 |
Claims
1. An image processing method comprising: at least one of recording
an image onto a thermoreversible recording medium in which
transparency or color tone reversibly changes depending upon
temperature, by applying a laser beam with the use of a
semiconductor laser device so as to heat the thermoreversible
recording medium, and erasing an image recorded on the
thermoreversible recording medium, by heating the thermoreversible
recording medium, wherein an intensity distribution of the laser
beam applied in the image recording step satisfies the relationship
represented by Expression 1 shown below,
1.20.ltoreq.I.sub.1/I.sub.2.ltoreq.1.29, Expression 1 where I.sub.1
denotes an irradiation intensity of the applied laser beam in a
central position of the applied laser beam, and I.sub.2 denotes an
irradiation intensity of the applied laser beam on a plane
corresponding to 95% of the total irradiation energy of the applied
laser beam.
2. The image processing method according to claim 1, wherein the
step of erasing an image is carried out by applying a laser beam so
as to heat the thermoreversible recording medium.
3. The image processing method according to claim 1, wherein the
thermoreversible recording medium comprises at least a support, and
a thermoreversible recording layer over the support; and the
transparency or color tone of the thermoreversible recording layer
reversibly changes at a first specific temperature and at a second
specific temperature higher than the first specific
temperature.
4. The image processing method according to claim 3, wherein the
thermoreversible recording layer contains a resin and a
low-molecular organic material.
5. The image processing method according to claim 3, wherein the
thermoreversible recording layer contains a leuco dye and a
reversible developer.
6. The image processing method according to claim 1, wherein the
thermoreversible recording medium contains a photothermal
conversion material.
7. The image processing method according to claim 6, wherein a
thermoreversible recording layer contains the photothermal
conversion material.
8. The image processing method according to claim 6, wherein the
photothermal conversion material is a phthalocyanine compound.
9. The image processing method according to claim 1, being used for
at least one of recording an image onto a moving object and erasing
an image from the moving object.
10. An image processing apparatus comprising: a laser beam emitting
unit that is a semiconductor laser device, a beam scanning unit
disposed on a surface from which a laser beam is emitted in the
laser beam emitting unit, a beam condensing unit configured to
condense a laser beam, and an irradiation intensity distribution
adjusting unit configured to change an irradiation intensity
distribution of a laser beam, wherein the image processing
apparatus is used in an image processing method which comprises at
least one of recording an image onto a thermoreversible recording
medium in which transparency or color tone reversibly changes
depending upon temperature, by applying a laser beam with the use
of the semiconductor laser device so as to heat the
thermoreversible recording medium, and erasing an image recorded on
the thermoreversible recording medium, by heating the
thermoreversible recording medium, wherein the intensity
distribution of the laser beam applied in the image recording step
satisfies the relationship represented by Expression 1 shown below,
1.20.ltoreq.I.sub.1/I.sub.2.ltoreq.1.29, Expression 1 where I.sub.1
denotes an irradiation intensity of the applied laser beam in a
central position of the applied laser beam, and I.sub.2 denotes an
irradiation intensity of the applied laser beam on a plane
corresponding to 95% of the total irradiation energy of the applied
laser beam.
11. The image processing apparatus according to claim 10, wherein
the irradiation intensity distribution adjusting unit is at least
any one of a lens, a filter, a mask, a fiber coupling and a
mirror.
12. The image processing apparatus according to claim 11, wherein
the lens is at least one of an aspheric element lens and a
diffractive optical element.
13. The image processing apparatus according to claim 10, wherein
the laser beam emitting unit is a semiconductor laser diode and the
image processing apparatus further comprises a cooling unit
configured to cool the semiconductor laser diode while measuring
and controlling the temperature of the semiconductor laser
diode.
14. The image processing apparatus according to claim 10, wherein
the laser beam emitting unit is a semiconductor laser diode, which
has emission wavelengths of 0.70 .mu.m to 1.55 .mu.m.
15. The image processing apparatus according to claim 10, wherein
the beam scanning unit is a galvano mirror, and the beam condensing
unit is an f.theta. lens.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an image processing method
capable of repeatedly recording and erasing a high-contrast image
at high speed by uniformly recording the image at high density and
uniformly erasing the image in a short period of time; and an image
processing apparatus which can be suitably used in the image
processing method.
[0003] 2. Description of the Related Art
[0004] As a method for recording and erasing an image onto and from
a thermoreversible recording medium (hereinafter otherwise referred
to as "reversible thermosensitive recording medium", "recording
medium" or "medium") from a distance or when depressions and
protrusions are created on the surface of the thermoreversible
recording medium, there has been proposed a method using a
noncontact laser (refer to Japanese Patent Application Laid-Open
(JP-A) No. 2000-136022). This proposal discloses that noncontact
recording is performed utilizing a reversible thermosensitive
recording medium as a transport container used in a product
distribution line, and that writing is carried out using a laser
and erasure is carried out using hot air, warm water, an infrared
heater or the like.
[0005] Additionally, recording methods each using a laser are
disclosed, for example, in Japanese Patent (JP-B) Nos. 3350836 and
3446316 and JP-A Nos. 2002-347272 and 2004-195751.
[0006] The technique described in JP-B No. 3350836 is related to a
modified image recording and erasing method including placing a
photothermal conversion sheet on a thermoreversible recording
medium, then irradiating the photothermal conversion sheet with a
laser beam, and forming or erasing an image on the thermoreversible
recording medium by means of the heat generated. In the
specification thereof, it is disclosed that both formation and
erasure of an image can be carried out by controlling the
irradiation conditions of a laser beam. Specifically, it is
disclosed that by controlling at least one of the irradiation time,
the irradiation luminosity, the focus and the intensity
distribution, it is possible to control the heating temperature in
a manner that is divided into a first specific temperature and a
second specific temperature of the thermoreversible recording
medium, and by changing the cooling rate after heating, it is
possible to form and erase an image on the whole surface or
partially.
[0007] JP-B No. 3446316 describes use of two laser beams and the
following methods: a method in which erasure is carried out with
one laser beam being used as an elliptical or oval laser beam, and
recording is carried out with the other laser beam being used as a
circular laser beam; a method in which recording is carried out
with the two laser beams being used in combination; and a method in
which recording is carried out, with each of the two laser beams
being modified and then these modified laser beams being used in
combination. According to these methods, use of the two laser beams
makes it possible to realize higher density image recording than
use of one laser beam does.
[0008] Additionally, the technique described in JP-A No.
2002-347272 is related to a method in which at the time of laser
recording and erasure, the front and back of one mirror are
utilized, and the form of the luminous flux of a laser beam is
changed depending upon the optical path difference and the form of
the mirror. Thus, the size of an optical spot can be changed and
defocusing is made possible with a simple optical system.
[0009] Further, JP-A No. 2004-195751 discloses that a residual
image after erasure can be removed substantially completely by
employing the following conditions: the laser absorption rate of a
reversible thermosensitive recording medium in the form of a label
is 50% or more; the irradiation energy is 5.0 mJ/mm.sup.2 to 15.0
mJ/mm.sup.2, and the product of the laser absorption rate and the
printing irradiation energy is 3.0 mJ/mm.sup.2 to 14.0 mJ/mm.sup.2,
at the time of printing; and the product of the laser absorption
rate and the printing irradiation energy at the time of erasure is
1.1 times to 3.0 times the above-mentioned product.
[0010] Meanwhile, as an image erasing method using a laser, JP-A
No. 2003-246144, for example, proposes a method in which an image
with clear contrast can be recorded onto a highly durable
reversible thermosensitive recording medium by erasing the image
such that the energy of a laser beam, the irradiation time of the
laser beam and the pulse width scanning speed at the time of
erasure are 25% to 65% of those at the time of laser recording.
[0011] According to the above-mentioned methods, images can be
recorded and erased by the lasers; however, since laser control is
not taken at the time of recording, there is a problem that local
thermal damage arises at places where lines overlap at the time of
recording, and there is a problem that the color-developing density
decreases when solid images are recorded.
[0012] With the intention of solving these problems, methods of
controlling printing energy are disclosed in JP-A Nos. 2003-127446
and 2004-345273.
[0013] JP-A No. 2003-127446 describes the following: laser
irradiation energy is controlled for every written point, and when
printing is performed such that recording dots overlap or printing
is performed onto a folded material, the amount of energy applied
thereto is reduced; also, when linear printing is performed, the
amount of energy is reduced at predetermined intervals so as to
lessen local thermal damage and thereby to prevent degradation of a
reversible thermosensitive recording medium.
[0014] Meanwhile, in JP-A No. 2004-345273, an attempt is made to
reduce energy at the time of laser writing, by multiplying the
irradiation energy by the expression |cos
0.5R|.sup.k(0.3<k<4), where R denotes the angle of a
varied-angle point. This makes it possible at the time of laser
recording to prevent excessive energy from being applied to a part
where linear images overlap and thereby to reduce degradation of a
medium, or to maintain contrast without reducing energy too
much.
[0015] Additionally, as a method for preventing decrease in
color-developing density, JP-A Nos. 2004-1264 proposes a method in
which in order to prevent a previously recorded image from being
erased when additional writing is carried out using a laser, the
dot arrangement pitch for sub scanning is made two or more times
greater than the color-developing radius of a laser beam and less
than or equal to the sum of the color-erasing radius and the
color-developing radius of the laser beam, thereby preventing
decrease in color-developing density and creation of a trace of
erasure.
[0016] As just described, in the above-mentioned methods, attempts
are made to avoid application of excessive thermal energy to
thermoreversible recording media, caused by overlapping at the time
of laser recording. Also, since the intensity distribution of a
laser beam is generally in the form of a Gaussian distribution in
which the central part of the laser beam is great in intensity,
written lines can be changed in width by adjusting the irradiation
power, without needing to change the irradiation distance. However,
since the energy of the central part becomes extremely high,
excessive energy is applied to a thermoreversible recording medium,
and when recording and erasure are repeatedly carried out, the
thermoreversible recording medium degrades at portions
corresponding to the central part.
[0017] As a result of carrying out a series of earnest examinations
so as to solve the above-mentioned problems, the present inventors
have previously proposed an image processing method and an image
processing apparatus, wherein in the intensity distribution of a
laser beam in a cross section substantially perpendicular to the
proceeding direction of the laser beam, the irradiation intensity
of the central part needs to be approximately equal to or less than
that of the surrounding part, with the phrase "approximately equal
to or less than" denoting 1.05 or less times, and the irradiation
intensity of the central part is preferably 1.03 or less times that
of the surrounding part, and more preferably 1.0 or less time;
ideally, the irradiation intensity of the central part is lower
than, namely less than 1.0 time, that of the surrounding part (JP-A
No. 2007-69605). Here, for the definitions of the central part and
the surrounding part, the paragraph [0021] in JP-A No. 2007-69605
states that "in the intensity distribution of the laser beam in the
cross section substantially perpendicular to the proceeding
direction of the laser beam, the `central part` denotes a site
corresponding to an area sandwiched between the apical portions of
two maximum peaks in the shape of inverted convexities, included in
a differential curve formed when a curve representing the intensity
distribution is differentiated twice; and the `surrounding part`
denotes a site corresponding to an area other than the `central
part`.
[0018] In JP-A No. 2007-69605, since the intensity distribution is
provided in which the irradiation intensity of the central part of
the laser beam is approximately equal to or less than that of the
surrounding part, uniform energy can be applied to a
thermoreversible recording medium, and thus the thermoreversible
recording medium does not degrade much even when recording and
erasure are repeatedly carried out. However, in such an intensity
distribution written lines can hardly be changed in width on a
thermoreversible recording medium by changing the irradiation
power. In order to change the written lines in width, the spot
diameter of the laser beam should be changed by changing the
irradiation distance. Thus, it is necessary to move a laser device
or the thermoreversible recording medium.
[0019] Moreover, due to variation in irradiation power; as to a
laser beam exhibiting an intensity distribution in the form of a
Gaussian distribution in which the central part of the laser beam
is high in irradiation intensity, recording is not hindered even
when the irradiation power is slightly reduced, because the
irradiation intensity of the central part is high enough, whereas
as to a laser beam exhibiting an intensity distribution in which
the irradiation intensity of the central part of the laser beam is
approximately equal to or less than that of the surrounding part,
there is a problem that recording may not take place when the
irradiation power is reduced.
[0020] Thus, as things stand at present, provision of an image
processing method and an image processing apparatus is hoped for,
wherein a thermoreversible recording medium can be uniformly
heated, excessive energy is not applied to the thermoreversible
recording medium, degradation of the thermoreversible recording
medium can be reduced when recording and erasure are repeatedly
carried out, durability against repeated use can be improved, and
written lines can be changed in width by adjusting the irradiation
power, without needing to change the irradiation distance.
BRIEF SUMMARY OF THE INVENTION
[0021] An object of the present invention is to provide an image
processing method and an image processing apparatus, wherein a
thermoreversible recording medium can be uniformly heated,
excessive energy is not applied to the thermoreversible recording
medium, degradation of the thermoreversible recording medium can be
reduced when recording and erasure are repeatedly carried out,
durability against repeated use can be improved, and written lines
can be changed in width by adjusting the irradiation power, without
needing to change the irradiation distance.
[0022] Means for solving the above-mentioned problems are as
follows.
[0023] <1> An image processing method including at least one
of recording an image onto a thermoreversible recording medium in
which transparency or color tone reversibly changes depending upon
temperature, by applying a laser beam with the use of a
semiconductor laser device so as to heat the thermoreversible
recording medium, and erasing an image recorded on the
thermoreversible recording medium, by heating the thermoreversible
recording medium, wherein an intensity distribution of the laser
beam applied in the image recording step satisfies the relationship
represented by Expression 1 shown below,
1.20.ltoreq.I.sub.1/I.sub.2.ltoreq.1.29 Expression 1
where I.sub.1 denotes an irradiation intensity of the applied laser
beam in a central position of the applied laser beam, and I.sub.2
denotes an irradiation intensity of the applied laser beam on a
plane corresponding to 95% of the total irradiation energy of the
applied laser beam.
[0024] <2> The image processing method according to
<1>, wherein the step of erasing an image is carried out by
applying a laser beam so as to heat the thermoreversible recording
medium.
[0025] <3> The image processing method according to any one
of <1> to <2>, wherein the thermoreversible recording
medium contains at least a support, and a thermoreversible
recording layer over the support; and the transparency or color
tone of the thermoreversible recording layer reversibly changes at
a first specific temperature and at a second specific temperature
higher than the first specific temperature.
[0026] <4> The image processing method according to
<3>, wherein the thermoreversible recording layer contains a
resin and a low-molecular organic material.
[0027] <5> The image processing method according to
<3>, wherein the thermoreversible recording layer contains a
leuco dye and a reversible developer.
[0028] <6> The image processing method according to any one
of <1> to <5>, wherein the thermoreversible recording
medium contains a photothermal conversion material.
[0029] <7> The image processing method according to
<6>, wherein the thermoreversible recording layer contains
the photothermal conversion material.
[0030] <8> The image processing method according to any one
of <6> to <7>, wherein the photothermal conversion
material is a phthalocyanine compound.
[0031] <9> The image processing method according to any one
of <1> to <8>, being used for at least one of recording
an image onto a moving object and erasing an image from the moving
object.
[0032] <10> An image processing apparatus includes a laser
beam emitting unit that is a semiconductor laser device, a beam
scanning unit disposed on a surface from which a laser beam is
emitted in the laser beam emitting unit, a beam condensing unit
configured to condense a laser beam and an irradiation intensity
distribution adjusting unit configured to change an irradiation
intensity distribution of a laser beam, wherein the image
processing apparatus is used in the image processing method
according to any one of <1> to <9>.
[0033] <11> The image processing apparatus according to
<10>, wherein the irradiation intensity distribution
adjusting unit is at least any one of a lens, a filter, a mask, a
fiber coupling and a mirror.
[0034] <12> The image processing apparatus according to
<11>, wherein the lens is at least one of an aspheric element
lens and a diffractive optical element.
[0035] <13> The image processing apparatus according to any
one of <10> and <12>, wherein the laser beam emitting
unit is a semiconductor laser diode and the image processing
apparatus further contains a cooling unit configured to cool the
semiconductor laser diode while measuring and controlling the
temperature of the semiconductor laser diode.
[0036] <14> The image processing apparatus according to any
one of <10> to <13>, wherein the laser beam emitting
unit is a semiconductor laser diode, which has emission wavelengths
of 0.70 .mu.m to 1.55 .mu.m.
[0037] <15> The image processing apparatus according to any
one of <10> to <14>, wherein the beam scanning unit is
a galvano mirror, and the beam condensing unit is an f.theta.
lens.
[0038] The image processing method of the present invention
includes at least one of recording an image onto a thermoreversible
recording medium in which transparency or color tone reversibly
changes depending upon temperature, by applying a laser beam with
the use of a semiconductor laser device so as to heat the
thermoreversible recording medium, and erasing an image recorded on
the thermoreversible recording medium, by heating the
thermoreversible recording medium, wherein an intensity
distribution of the laser beam applied in the image recording step
satisfies the relationship represented by Expression 1 shown
below,
1.20.ltoreq.I.sub.1/I.sub.2.ltoreq.1.29 Expression 1
where I.sub.1 denotes an irradiation intensity of the applied laser
beam in a central position of the applied laser beam, and I.sub.2
denotes an irradiation intensity of the applied laser beam on a
plane corresponding to 95% of the total irradiation energy of the
applied laser beam.
[0039] As to the image processing method of the present invention,
the intensity distribution of the laser beam applied in the image
recording step satisfies the relationship represented by the
expression 1.20.ltoreq.I.sub.1/I.sub.2.ltoreq.1.29 (where I.sub.1
denotes the irradiation intensity of the applied laser beam in a
central position of the applied laser beam, and I.sub.2 denotes the
irradiation intensity of the applied laser beam on a plane
corresponding to 95% of the total irradiation energy of the applied
laser beam); thus, excessive energy is not applied to a
thermoreversible recording medium, degradation of the
thermoreversible recording medium can be reduced when recording and
erasure are repeatedly carried out, durability against repeated use
can be improved, and written lines can be changed in width by
adjusting the irradiation power, without needing to change the
irradiation distance.
[0040] The image processing apparatus of the present invention is
used in the image processing method of the present invention and
contains at least a laser beam emitting unit, a beam scanning unit,
a beam condensing unit and an irradiation intensity distribution
adjusting unit.
[0041] In the image processing apparatus, a semiconductor laser
device serving as the laser beam emitting unit emits a laser beam.
The irradiation intensity distribution adjusting unit changes the
intensity of a laser beam emitted from the laser beam emitting
unit, such that the ratio (I.sub.1/I.sub.2) satisfies
1.20.ltoreq.I.sub.1/I.sub.2.ltoreq.1.29 (where I.sub.1 denotes the
irradiation intensity of the applied laser beam in a central
position of the applied laser beam, and I.sub.2 denotes the
irradiation intensity of the applied laser beam on a plane
corresponding to 95% of the total irradiation energy of the applied
laser beam). Consequently, excessive energy is not applied to a
thermoreversible recording medium, degradation of the
thermoreversible recording medium can be reduced when recording and
erasure are repeatedly carried out, durability against repeated use
can be improved, and written lines can be changed in width by
adjusting the irradiation power, without needing to change the
irradiation distance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] FIG. 1 is a schematic explanatory diagram showing an example
of the intensity distribution of an applied laser beam used in the
present invention.
[0043] FIG. 2A is a schematic explanatory diagram showing the
intensity distribution (Gaussian distribution) of a laser beam in
its normal state.
[0044] FIG. 2B is a schematic explanatory diagram showing an
example of the intensity distribution of the laser beam when the
intensity distribution has been changed.
[0045] FIG. 2C is a schematic explanatory diagram showing another
example of the intensity distribution of the laser beam when the
intensity distribution has been changed.
[0046] FIG. 2D is a schematic explanatory diagram showing yet
another example of the intensity distribution of the laser beam
when the intensity distribution has been changed.
[0047] FIG. 3 is a diagram for explaining an example of an image
processing apparatus of the present invention.
[0048] FIG. 4A is a graph showing the transparency--white turbidity
properties of a thermoreversible recording medium.
[0049] FIG. 4B is a schematic explanatory diagram showing the
mechanism of a transparency--white turbidity change of a
thermoreversible recording medium.
[0050] FIG. 5A is a graph showing the color developing--color
erasing properties of a thermoreversible recording medium.
[0051] FIG. 5B is a schematic explanatory diagram showing the
mechanism of a color developing--color erasing change of the
thermoreversible recording medium.
[0052] FIG. 6 is a schematic diagram showing an example of an RF-ID
tag.
[0053] FIG. 7 is a diagram for explaining an example of an aspheric
element lens used in the present invention.
DETAILED DESCRIPTION OF THE INVENTION
(Image Processing Method)
[0054] An image processing method of the present invention includes
at least one of an image recording step and an image erasing step,
and further includes other steps suitably selected in accordance
with the necessity.
[0055] The image processing method of the present invention
includes all of the following aspects: an aspect in which both
recording and erasure of an image are performed, an aspect in which
only recording of an image is performed, and an aspect in which
only erasure of an image is performed.
<Image Recording Step and Image Erasing Step>
[0056] The image recording step in the image processing method of
the present invention is a step of recording an image onto a
thermoreversible recording medium in which transparency or color
tone reversibly changes depending upon temperature, by applying a
laser beam with the use of a semiconductor laser device so as to
heat the thermoreversible recording medium.
[0057] The image erasing step in the image processing method of the
present invention is a step of erasing an image recorded on the
thermoreversible recording medium, by heating the thermoreversible
recording medium.
[0058] For a heat source used at the time of heating, a laser beam
or other heat sources may be used. As to such heat sources, in the
case where the thermoreversible recording medium is heated by laser
beam irradiation, it takes a long time to irradiate the whole of a
predetermined area by scanning with one laser beam; accordingly, to
erase an image in a short time, it is desirable to erase it by
heating the thermoreversible recording medium with the use of an
infrared lamp, a heat roller, a hot stamp, a dryer or the like.
Also, in the case where the thermoreversible recording medium is
mounted on a Styrofoam box serving as a transport container used in
a product distribution line, if the Styrofoam box itself is heated,
it will melt, and thus it is desirable to erase an image by
applying a laser beam so as to heat only the thermoreversible
recording medium locally.
[0059] By applying the laser beam so as to heat the
thermoreversible recording medium, it is possible to record and
erase an image onto the thermoreversible recording medium in a
noncontact manner.
[0060] In the image processing method of the present invention,
normally, an image is renewed for a first time when the
thermoreversible recording medium is reused (the above-mentioned
image erasing step), then an image is recorded by the image
recording step; however, recording and erasure of an image do not
necessarily have to follow this order, and an image may be recorded
by the image recording step first and then erased by the image
erasing step.
[0061] In the present invention, an intensity distribution of the
laser beam applied in the image recording step satisfies the
relationship represented by Expression 1 shown below.
1.20.ltoreq.I.sub.1/I.sub.2.ltoreq.1.29 Expression 1
where I.sub.1 denotes an irradiation intensity of the applied laser
beam in a central position of the applied laser beam, and I.sub.2
denotes an irradiation intensity of the applied laser beam on a
plane corresponding to 95% of the total irradiation energy of the
applied laser beam.
[0062] When the intensity distribution of an applied laser beam is
divided by a horizontal plane with regard to a travelling direction
in an orthogonal direction, such that the maximum value of the
intensity is included in the region occupying 5% of the total
irradiation energy, the irradiation intensity of the applied laser
beam on the horizontal plane is defined as I.sub.2, an irradiation
intensity of the applied laser beam in a central position of the
applied laser beam is defined as I.sub.1, and the ratio
(I.sub.1/I.sub.2) is 1.43 given by Gaussian distribution (normal
distribution).
[0063] Here, as shown in FIG. 1, the "plane corresponding to 95% of
the total irradiation energy of the applied laser beam" means a
horizontal dividing plane, in the case where the irradiation
intensity of the laser beam is measured using a high-power beam
analyzer with a high-sensitivity pyroelectric camera, the obtained
irradiation intensity is formed into a three-dimensional graph, and
the irradiation intensity distribution is divided into two regions
such that the region sandwiched between the plane where z=0 and the
dividing plane which is horizontal to the plane where z=0 occupies
95% of the total irradiation energy. On this occasion, the Z axis
denotes the irradiation intensity of the applied laser beam.
[0064] The total irradiation energy means the total energy of a
laser beam applied onto a thermoreversible recording medium.
[0065] The central position of the applied laser beam is a position
which can be calculated by dividing the summation of the product of
the irradiation intensity in each position and the coordinates at
each position by the summation of the irradiation intensity in each
position. The position can be represented by the following
expression.
.SIGMA.(ri.times.Ii)/.SIGMA.Ii
[0066] Note that "ri" denotes the coordinates at each position,
"I.sub.i" denotes the irradiation intensity in each position, and
".SIGMA.Ii" denotes the total irradiation intensity.
[0067] FIGS. 2A to 2D each show an example of an intensity
distribution curve of an applied laser beam in a cross section
including the maximum value, when the intensity distribution has
been changed. FIG. 2A shows a Gaussian distribution; in such an
intensity distribution in which the central part of the laser beam
is high in irradiation intensity, I.sub.2 is low with respect to
I.sub.1, and thus the ratio (I.sub.1/I.sub.2) is large. Meanwhile,
as shown in FIG. 2B, in an intensity distribution in which the
central part of the laser beam is lower in irradiation intensity
than that in the intensity distribution of FIG. 2A, I.sub.2 is
large with respect to I.sub.1, and thus the ratio (I.sub.1/I.sub.2)
is lower than that in the intensity distribution of FIG. 2A. In an
intensity distribution having a form similar to that of a top hat,
as shown in FIG. 2C, I.sub.2 further increases with respect to
I.sub.1, and thus the ratio (I.sub.1/I.sub.2) is even lower than
that in the intensity distribution of FIG. 2B. In an intensity
distribution in which the central part of the laser beam is low in
irradiation intensity and the surrounding part is high in
irradiation intensity, as shown in FIG. 2D, I.sub.1 decreases with
respect to I.sub.2, and thus the ratio (I.sub.1/I.sub.2) is even
lower than that in the intensity distribution of FIG. 2C. Hence,
the ratio (I.sub.1/I.sub.2) indicates the form of the irradiation
intensity distribution of the laser beam.
[0068] In the present invention, when the ratio (I.sub.1/I.sub.2)
is less than or equal to 1.20, there is an intensity distribution
in the form of a top hat or in which the irradiation intensity of
the central part is lower than that of the surrounding part; thus,
degradation of a thermoreversible recording medium caused by
repeated use can be reduced, and erasure of an image is possible
even when recording and erasure are repeatedly carried out;
however, written lines cannot be changed in width unless the
irradiation distance is changed, and if the ratio (I.sub.1/I.sub.2)
further decreases, the irradiation intensity of the central part is
so low that when an image is recorded, a line may split in two
without developing the color of its central part.
[0069] When the ratio (I.sub.1/I.sub.2) is greater than 1.29,
written lines can be changed in width by adjusting the irradiation
power, without needing to change the irradiation distance; however,
excessive energy is applied to a thermoreversible recording medium,
and when recording and erasure are repeatedly carried out, there
may be an unerased portion left owing to degradation of the
thermoreversible recording medium.
[0070] The ratio (I.sub.1/I.sub.2) preferably satisfies
1.20.ltoreq.I.sub.1/I.sub.2.ltoreq.1.29, and more preferably
satisfies 1.20.ltoreq.I.sub.1/I.sub.2.ltoreq.1.25.
[0071] In the present invention, a semiconductor laser is used as
the laser beam emitting unit, and a laser beam therefrom is
adsorbed in a photothermal conversion layer or a recording layer in
which a photothermal conversion material is added, and thermal
diffusion enables to easily make the temperature distribution in
the recording layer uniform.
[0072] In the present invention, it is important in the irradiation
intensity distribution of the laser beam that the ratio
(I.sub.1/I.sub.2) be within a specific range, where "I.sub.1"
denotes the irradiation intensity of the laser beam in a central
position of the laser beam, and "I.sub.2" denotes the minimum value
in a region which includes a peak of the energy distribution and a
certain percentage of the total irradiation energy of the applied
laser beam.
[0073] The method of making the ratio (I.sub.1/I.sub.2) satisfy
1.20.ltoreq.I.sub.1/I.sub.2.ltoreq.1.29, is not particularly
limited and may be suitably selected in accordance with the
intended use; for instance, an irradiation intensity distribution
adjusting unit can be suitably used. The irradiation intensity
distribution adjusting unit will be described later.
[0074] The spot diameter of the laser beam applied in the image
recording step is preferably 0.05 mm to 5.0 mm.
[0075] The method for changing the intensity distribution of the
laser beam so as to satisfy the ratio (I.sub.1/I.sub.2) represented
by the expression: 1.20.ltoreq.I.sub.1/I.sub.2.ltoreq.1.29, is not
particularly limited and may be suitably selected in accordance
with the intended use; for instance, an irradiation intensity
distribution adjusting unit can be suitably used.
[0076] The irradiation intensity distribution adjusting unit is not
particularly limited and may be suitably selected in accordance
with the intended use. Suitable examples thereof include lenses,
filters, masks, mirrors and fiber couplings. Among these, lenses
are preferable because of causing less energy loss. Examples of
lenses include kaleidoscopes, integrators, aspheric element lenses,
beam homogenizers, aspheric beam shapers (each of which is a
combination of an intensity transformation lens and a phase
correction lens), and diffractive optical elements. Among these,
aspheric element lenses and diffractive optical elements are
particularly preferable.
[0077] When a filter, a mask or the like is used, the irradiation
intensity can be adjusted by physically cutting a central part of
the laser beam. Meanwhile, when a mirror is used, the irradiation
intensity can be adjusted by using, for example, a deformable
mirror that is linked to a computer and can be mechanically changed
in shape, or a mirror in which the reflectance or the formation of
depressions and protrusions on the surface varies from part to
part. A semiconductor laser having emission wavelengths of visible
light to near infrared light is preferably used, because the
irradiation intensity of an applied laser beam is easily adjusted
by fiber coupling.
[0078] The output of the laser beam applied in the image recording
step is not particularly limited and may be suitably selected in
accordance with the intended use; however, it is preferably 1 W or
greater, more preferably 3 W or greater, and even more preferably 3
W or greater. When the output of the laser beam is less than 1 W,
it takes a long time to record an image, and if an attempt is made
to reduce the time spent on image recording, a high-density image
cannot be obtained because of a lack of output. Additionally, the
upper limit of the output of the laser beam is not particularly
limited and may be suitably selected in accordance with the
intended use; however, it is preferably 200 W or less, more
preferably 150 W or less, and even more preferably 100 W or less.
When the output of the laser beam is greater than 200 W, it leads
to an increase in the size of a laser device.
[0079] The scanning speed of the laser beam applied in the image
recording step is not particularly limited and may be suitably
selected in accordance with the intended use; however, it is
preferably 300 mm/s or greater, more preferably 500 mm/s or
greater, and even more preferably 700 mm/s or greater. When the
scanning speed is less than 300 mm/s, it takes a long time to
record an image. Additionally, the upper limit of the scanning
speed of the laser beam is not particularly limited and may be
suitably selected in accordance with the intended use; however, it
is preferably 15,000 mm/s or less, more preferably 10,000 mm/s or
less, and even more preferably 8,000 mm/s or less. When the
scanning speed is higher than 15,000 mm/s, it is difficult to
record a uniform image.
[0080] The spot diameter of the laser beam applied in the image
recording step is not particularly limited and may be suitably
selected in accordance with the intended use; however, it is
preferably 0.02 mm or greater, more preferably 0.1 mm or greater,
and even more preferably 0.15 mm or greater.
[0081] Additionally, the upper limit of the spot diameter of the
laser beam is not particularly limited and may be suitably selected
in accordance with the intended use; however, it is preferably 3.0
mm or less, more preferably 2.5 mm or less, and even more
preferably 2.0 mm or less.
[0082] When the spot diameter is small, the line width of an image
is also thin, and the contrast of the image lowers, thereby causing
a decrease in visibility. When the spot diameter is large, the line
width of an image is also thick, and adjacent lines overlap,
thereby making it impossible to print small letters/characters.
[0083] The output of a laser beam applied in the image erasing step
where a recorded image is erased by applying a laser beam so as to
heat the thermoreversible recording medium is not particularly
limited and may be suitably selected in accordance with the
intended use; however, it is preferably 5 W or greater, more
preferably 7 W or greater, and even more preferably 10 W or
greater. When the output of the leaser beam is less than 5 W, it
takes some time to erase a recorded image, and if an attempt is
made to reduce the time spent on image erasing, an image erasing
defect occurs because of a lack of the output. Additionally, the
upper limit of the output of the laser beam is not particularly
limited and may be suitably selected in accordance with the
intended use; however, it is preferably 200 W or less, more
preferably 150 W or less, and even more preferably 100 W or less.
When the output of the laser beam is more than 200 W, it leads to
an increase in the size of a laser device.
[0084] The scanning speed of a laser beam applied in the image
erasing step where a recorded image is erased by applying a laser
beam so as to heat the thermoreversible recording medium is not
particularly limited and may be suitably selected in accordance
with the intended use; however, it is preferably 100 mm/s or
greater, more preferably 200 mm/s or greater, and even more
preferably 300 mm/s or greater. When the scanning speed is less
than 100 mm/s, it takes some time to erase a recorded image.
Additionally, the upper limit of the scanning speed of the laser
beam is not particularly limited and may be suitably selected in
accordance with the intended use; however, it is preferably 20,000
mm/s or less, more preferably 15,000 mm/s or less, and even more
preferably 10,000 mm/s or less. When the scanning speed is higher
than 20,000 mm/s, it is difficult to uniformly erase a recorded
image.
[0085] The spot diameter of a laser beam applied in the image
erasing step where a recorded image is erased by applying a laser
beam so as to heat the thermoreversible recording medium is not
particularly limited and may be suitably selected in accordance
with the intended use; however, it is preferably 0.5 mm or greater,
more preferably 1.0 mm or greater, and even more preferably 2.0 mm
or greater.
[0086] Additionally, the upper limit of the spot diameter of the
laser beam is not particularly limited and may be suitably selected
in accordance with the intended use; however, it is preferably 14.0
mm or less, more preferably 10.0 mm or less, and still more
preferably 7.0 mm or less.
[0087] When the spot diameter is small, it takes some time to erase
a recorded image. When the spot diameter is large, an image erasing
defect may occur because of a lack of the output.
[0088] As a laser that emits the laser beam, a semiconductor laser
is used.
[0089] The method for measuring the intensity distribution of the
laser beam is not particularly limited and may be suitably selected
as long as the intensity distribution of a semiconductor laser beam
can be measured; however, use of a device capable of measuring it
with a resolution of 10 .mu.m or less is preferable because the
accuracy of the intensity distribution measurement can be
enhanced.
<Image Recording and Image Erasing Mechanism>
[0090] The image recording and image erasing mechanism includes an
aspect in which transparency reversibly changes depending upon
temperature, and an aspect in which color tone reversibly changes
depending upon temperature.
[0091] In the aspect in which transparency reversibly changes
depending upon temperature, the low-molecular organic material in
the thermoreversible recording medium is dispersed in the form of
particles in the resin, and the transparency reversibly changes by
heat between a transparent state and a white turbid state.
[0092] The change in the transparency is viewed based upon the
following phenomena. In the case of the transparent state (1),
particles of the low-molecular organic material dispersed in a
resin base material and the resin base material are closely
attached to each other without spaces, and there is no void inside
the particles; therefore, a beam that has entered from one side
permeates to the other side without diffusing, and thus the
thermoreversible recording medium appears transparent. Meanwhile,
in the case of the white turbid state (2), the particles of the
low-molecular organic material are formed by fine crystals of the
low-molecular organic material, and there are spaces (voids)
created at the interfaces between the crystals or the interfaces
between the particles and the resin base material; therefore, a
beam that has entered from one side is refracted at the interfaces
between the voids and the crystals or the interfaces between the
voids and the resin and thereby diffuses, and thus the
thermoreversible recording medium appears white.
[0093] First of all, an example of the temperature-transparency
change curve of a thermoreversible recording medium having a
thermoreversible recording layer (hereinafter otherwise referred to
as "recording layer") formed by dispersing the low-molecular
organic material in the resin is shown in FIG. 4A.
[0094] The recording layer is in a white turbid opaque state (A),
for example, at normal temperature that is lower than or equal to
the temperature T.sub.0. Once the recording layer is heated, it
gradually becomes transparent as the temperature exceeds the
temperature T.sub.1. When heated to a temperature between the
temperatures T.sub.2 and T.sub.3, the recording layer becomes
transparent (B). The recording layer remains transparent (D) even
if the temperature is brought back to normal temperature that is
lower than or equal to T.sub.0. This is attributed to the following
phenomena: when the temperature is in the vicinity of T.sub.1, the
resin starts to soften, then as the softening proceeds, the resin
contracts, and voids at the interfaces between the resin and
particles of the low-molecular organic material or voids inside
these particles are reduced, so that the transparency gradually
increases; at temperatures between T.sub.2 and T.sub.3, the
low-molecular organic material comes into a semi-melted state, and
the recording layer becomes transparent as remaining voids are
filled with the low-molecular organic material; when the recording
layer is cooled with seed crystals remaining, crystallization takes
place at a fairly high temperature; at this time, since the resin
is still in the softening state, the resin adapts to a volume
change of the particles caused by the crystallization, the voids
are not created, and the transparent state is maintained.
[0095] When further heated to a temperature higher than or equal to
the temperature T.sub.4, the recording layer comes into a
semitransparent state (C) that is between the maximum transparency
and the maximum opacity. Next, when the temperature is lowered, the
recording layer returns to the white turbid opaque state (A) it was
in at the beginning, without coming into the transparent state
again. It is inferred that this is because the low-molecular
organic material completely melts at a temperature higher than or
equal to T4, then comes into a supercooled state and crystallizes
at a temperature a little higher than T.sub.0, and on this
occasion, the resin cannot adapt to a volume change of the
particles caused by the crystallization, which leads to creation of
voids.
[0096] Here, in FIG. 4A, when the temperature of the recording
layer is repeatedly raised to the temperature T.sub.5 far higher
than T.sub.4, there may be caused such an erasure failure that an
image cannot be erased even if the recording layer is heated to an
erasing temperature. This is attributed to a change in the internal
structure of the recording layer caused by transfer of the
low-molecular organic material, which has been melted by heating,
in the resin. To reduce degradation of the thermoreversible
recording medium caused by repeated use, it is necessary to
decrease the difference between T.sub.4 and T.sub.5 in FIG. 4A when
the thermoreversible recording medium is heated; in the case where
a means of heating it is a laser beam, the ratio (I.sub.1/I.sub.2)
in the intensity distribution of the laser beam is preferably 1.29
or less, and more preferably 1.25 or less.
[0097] As to the temperature-transparency change curve shown in
FIG. 4A, it should be noted that when the type of the resin, the
low-molecular organic material, etc. is changed, the transparency
in the above-mentioned states may change depending upon the
type.
[0098] FIG. 4B shows the mechanism of change in the transparency of
the thermoreversible recording medium in which the transparent
state and the white turbid state reversibly change by heat.
[0099] In FIG. 4B, one long-chain low-molecular material particle
and a polymer around it are viewed, and changes related to creation
and disappearance of a void, caused by heating and cooling, are
shown. In a white turbid state (A), a void is created between the
polymer and the low-molecular material particle (or inside the
particle), and thus there is a state of light diffusion. When these
are heated to a temperature higher than the softening temperature
(Ts) of the polymer, the void decreases in size, and the
transparency thereby increases. When these are further heated to a
temperature close to the melting temperature (Tm) of the
low-molecular material particle, a part of the low-molecular
material particle melts; due to volume expansion of the
low-molecular material particle that has melted, the void
disappears as it is filled with the low-molecular material
particle, and a transparent state (B) is thus produced. When
cooling is carried out from this temperature, the low-molecular
material particle crystallizes immediately below the melting
temperature, a void is not created, and a transparent state (D) is
maintained even at room temperature.
[0100] Subsequently, when heating is carried out such that the
temperature becomes higher than or equal to the melting temperature
of the low-molecular material particle, there is created a
difference in refractive index between the low-molecular material
particle that has melted and the polymer around it, and a
semitransparent state (C) is thus produced. When cooling is carried
out from this temperature to room temperature, the low-molecular
material particle is supercooled and crystallizes at a temperature
lower than or equal to the softening temperature of the polymer; at
this time, the polymer around the low-molecular material particle
is in a glassy state and therefore cannot adapt to a volume
reduction of the low-molecular material particle caused by the
crystallization; thus a void is created, and the white turbid state
(A) is reproduced.
[0101] Next, in the aspect in which color tone reversibly changes
depending upon temperature, the low-molecular organic material
before melting is a leuco dye and a reversible developer
(hereinafter otherwise referred to as "developer"), and the
low-molecular organic material after melted and before
crystallization is the leuco dye and the reversible developer and
the color tone reversibly changes by heat between a transparent
state and a color-developed state.
[0102] FIG. 5A shows an example of the
temperature--color-developing density change curve of a
thermoreversible recording medium which has a thermoreversible
recording layer formed of the resin containing the leuco dye and
the developer. FIG. 5B shows the color-developing and color-erasing
mechanism of the thermoreversible recording medium which reversibly
changes by heat between a transparent state and a color-developed
state.
[0103] First of all, when the recording layer in a colorless state
(A) is raised in temperature, the leuco dye and the developer melt
and mix at the melting temperature T.sub.1, thereby developing
color, and the recording layer thusly comes into a melted and
color-developed state (B). When the recording layer in the melted
and color-developed state (B) is rapidly cooled, the recording
layer can be lowered in temperature to room temperature, with its
color-developed state kept, and it thusly comes into a
color-developed state (C) where its color-developed state is
stabilized and fixed. Whether or not this color-developed state is
obtained depends upon the temperature decreasing rate from the
temperature in the melted state: in the case of slow cooling, the
color is erased in the temperature decreasing process, and the
recording layer returns to the colorless state (A) it was in at the
beginning, or comes into a state where the density is low in
comparison with the density in the color-developed state (C)
produced by rapid cooling. When the recording layer in the
color-developed state (C) is raised in temperature again, the color
is erased at the temperature T.sub.2 lower than the
color-developing temperature (from D to E), and when the recording
layer in this state is lowered in temperature, it returns to the
colorless state (A) it was in at the beginning.
[0104] The color-developed state (C) obtained by rapidly cooling
the recording layer in the melted state is a state where the leuco
dye and the developer are mixed together such that their molecules
can undergo contact reaction, which is often a solid state. This
state is a state where a melted mixture (color-developing mixture)
of the leuco dye and the developer crystallizes, and thus color
development is maintained, and it is inferred that the color
development is stabilized by the formation of this structure.
Meanwhile, the colorless state is a state where the leuco dye and
the developer are phase-separated. It is inferred that this state
is a state where molecules of at least one of the compounds gather
to constitute a domain or crystallize, and thus a stabilized state
where the leuco dye and the developer are separated from each other
by the occurrence of the flocculation or the crystallization. In
many cases, phase separation of the leuco dye and the developer is
brought about, and the developer crystallizes in this manner,
thereby enabling color erasure with greater completeness.
[0105] As to both the color erasure by slow cooling from the melted
state and the color erasure by temperature increase from the
color-developed state shown in FIG. 5A, the aggregation structure
changes at T.sub.2, causing phase separation and crystallization of
the developer.
[0106] Further, in FIG. 5A, when the temperature of the recording
layer is repeatedly raised to the temperature T.sub.3 higher than
or equal to the melting temperature T.sub.1, there may be caused
such an erasure failure that an image cannot be erased even if the
recording layer is heated to an erasing temperature. It is inferred
that this is because the developer thermally decomposes and thus
hardly flocculates or crystallizes, which makes it difficult for
the developer to separate from the leuco dye. Degradation of the
thermoreversible recording medium caused by repeated use can be
reduced by decreasing the difference between the melting
temperature T.sub.1 and the temperature T.sub.3 in FIG. 5A when the
thermoreversible recording medium is heated.
[Thermoreversible Recording Medium]
[0107] The thermoreversible recording medium used in the image
processing method of the present invention includes at least a
support, a reversible thermosensitive recording layer and a
photothermal conversion layer, and further includes other layers
suitably selected in accordance with the necessity, such as a
protective layer, an intermediate layer, an oxygen blocking layer,
an undercoat layer, a back layer, an adhesion layer, a tackiness
layer, a colored layer, an air layer and a light-reflecting layer.
Each of these layers may have a single-layer structure or a
laminated structure.
[0108] The thermoreversible recording medium is necessary to have a
layer for absorbing a semiconductor laser beam, such as a
photothermal conversion layer or a recording layer in which a
photothermal conversion material is added.
--Support--
[0109] The shape, structure, size and the like of the support are
not particularly limited and may be suitably selected in accordance
with the intended use. Examples of the shape include plate-like
shapes; the structure may be a single-layer structure or a
laminated structure; and the size may be suitably selected
according to the size of the thermoreversible recording medium,
etc.
[0110] Examples of the material for the support include inorganic
materials and organic materials.
[0111] Examples of the inorganic materials include glass, quartz,
silicon, silicon oxide, aluminum oxide, SiO.sub.2 and metals.
[0112] Examples of the organic materials include paper, cellulose
derivatives such as cellulose triacetate, synthetic paper, and
films made of polyethylene terephthalate, polycarbonates,
polystyrene, polymethyl methacrylate, etc.
[0113] Each of the inorganic materials and the organic materials
may be used alone or in combination with two or more. Among these
materials, the organic materials are preferable, particularly films
made of polyethylene terephthalate, polycarbonates, polymethyl
methacrylate, etc. are preferable. Of these, polyethylene
terephthalate is particularly preferable.
[0114] It is desirable that the support be subjected to surface
modification by means of corona discharge, oxidation reaction
(using chromic acid, for example), etching, facilitation of
adhesion, antistatic treatment, etc. for the purpose of improving
the adhesiveness of a coating layer.
[0115] Also, it is desirable to color the support white by adding,
for example, a white pigment such as titanium oxide to the
support.
[0116] The thickness of the support is not particularly limited and
may be suitably selected in accordance with the intended use, with
the range of 10 .mu.m to 2,000 .mu.m being preferable and the range
of 50 .mu.m to 1,000 .mu.m being more preferable.
--Thermoreversible Recording Layer--
[0117] The thermoreversible recording layer (which may be
hereinafter referred to simply as "recording layer") includes at
least a material in which transparency or color tone reversibly
changes depending upon temperature, and further includes other
components in accordance with the necessity.
[0118] The material in which transparency or color tone reversibly
changes depending upon temperature is a material capable of
exhibiting a phenomenon in which visible changes are reversibly
produced by temperature change; and the material can relatively
change into a color-developed state and into a colorless state,
depending upon the heating temperature and the cooling rate after
heating. In this case, the visible changes can be classified into
changes in the state of color and changes in shape. The changes in
the state of color stem from changes in transmittance, reflectance,
absorption wavelength, the degree of diffusion, etc., for example.
The state of the color of the thermoreversible recording medium, in
effect, changes due to a combination of these changes.
[0119] The material in which transparency or color tone reversibly
changes depending upon temperature is not particularly limited and
may be suitably selected from known materials. For example, two or
more types of polymers are mixed and the color of the mixture
becomes transparent or white turbid depending on compatibility
(refer to JP-A 61-258853), a material taking advantage of phase
change of a liquid crystal polymer (refer to JP-A 62-66990), a
material which comes into a state of first color at a first
specific temperature which is higher than normal temperature, and
comes into a state of second color by heating at a second specific
temperature which is higher than the first specific temperature,
and then cooling.
[0120] Among the known materials, a material in which the color
changes according to the first specific temperature and the second
specific temperature is particularly preferable in that the
temperature can be easily controlled and high contrast can be
obtained.
[0121] Examples thereof include a material which comes into a
transparent state at a first specific temperature and comes into a
white turbid state at a second specific temperature (refer to JP-A
No. 55-154198); a material which develops color at a second
specific temperature and loses the color at a first specific
temperature (refer to JP-A Nos. 04-224996, 04-247985 and
04-267190); a material which comes into a white turbid state at a
first specific temperature and comes into a transparent state at a
second specific temperature (refer to JP-A No. 03-169590); and a
material which develops a color (black, red, blue, etc.) at a first
specific temperature and loses the color at a second specific
temperature (refer to JP-A Nos. 02-188293 and 02-188294).
[0122] Among these, a thermoreversible recording medium including a
resin base material and a low-molecular organic material such as a
higher fatty acid dispersed in the resin base material is
advantageous in that a second specific temperature and a first
specific temperature are relatively low, and so erasure and
recording can be performed with low energy. Also, since the
color-developing and color-erasing mechanism is a physical change
which depends upon solidification of the resin and crystallization
of the low-molecular organic material, the thermoreversible
recording medium offers high environment resistance.
[0123] Additionally, a thermoreversible recording medium, which
uses the after-mentioned leuco dye and reversible developer and
which develops color at a second specific temperature and loses the
color at a first specific temperature, exhibits a transparent state
and a color-developed state reversibly and exhibits black, blue or
other color in the color-developed state; therefore, a
high-contrast image can be obtained.
[0124] The low-molecular organic material (which is dispersed in
the resin base material and which comes into a transparent state at
the first specific temperature and comes into a white turbid state
at the second specific temperature) in the thermoreversible
recording medium is not particularly limited and may be suitably
selected in accordance with the intended use, as long as it can
change from a polycrystalline material to a single-crystal material
by heat in the recording layer. Generally, a material having a
melting temperature of approximately 30.degree. C. to 200.degree.
C. can be used therefor, preferably a material having a melting
temperature of 50.degree. C. to 150.degree. C.
[0125] Such a low-molecular organic material is not particularly
limited and may be suitably selected in accordance with the
intended use. Examples thereof include alkanols; alkanediols;
halogenated alkanols and halogenated alkanediols; alkylamines;
alkanes; alkenes; alkines; halogenated alkanes; halogenated
alkenes; halogenated alkines; cycloalkanes; cycloalkenes;
cycloalkines; saturated or unsaturated monocarboxylic/dicarboxylic
acids, esters thereof, amides thereof and ammonium salts thereof;
saturated or unsaturated halogenated fatty acids, esters thereof,
amides thereof and ammonium salts thereof; arylcarboxylic acids,
esters thereof, amides thereof and ammonium salts thereof;
halogenated arylcarboxylic acids, esters thereof, amides thereof
and ammonium salts thereof, thioalcohols; thiocarboxylic acids,
esters thereof, amines thereof and ammonium salts thereof; and
carboxylic acid esters of thioalcohols. Each of these may be used
alone or in combination with two or more.
[0126] Each of these compounds preferably has 10 to 60 carbon
atoms, more preferably 10 to 38 carbon atoms, most preferably 10 to
30 carbon atoms. Alcohol groups in the esters may or may not be
saturated, and may be halogen-substituted.
[0127] The low-molecular organic material preferably has in its
molecules at least one selected from oxygen, nitrogen, sulfur and
halogens, for example groups such as --OH, --COOH, --CONH--,
--COOR, --NH--, --NH.sub.2, --S--, --S--S-- and --O--, and halogen
atoms.
[0128] More specific examples of these compounds include higher
fatty acids such as lauric acid, dodecanoic acid, myristic acid,
pentadecanoic acid, palmitic acid, stearic acid, behenic acid,
nonadecanoic acid, arachidonic acid and oleic acid; and esters of
higher fatty acids such as methyl stearate, tetradecyl stearate,
octadecyl stearate, octadecyl laurate, tetradecyl palmitate and
dodecyl behenate. The low-molecular organic material used in the
third aspect of the image processing method is preferably selected
from higher fatty acids among these compounds, more preferably
higher fatty acids having 16 or more carbon atoms such as palmitic
acid, stearic acid, behenic acid and lignoceric acid, even more
preferably higher fatty acids having 16 to 24 carbon atoms.
[0129] To increase the range of temperatures at which the
thermoreversible recording medium can be made transparent, the
above-mentioned low-molecular organic materials may be suitably
combined together, or any of the above-mentioned low-molecular
organic materials may be combined with other material having a
different melting temperature. Use of such materials is disclosed
in JP-A Nos. 63-39378 and 63-130380, JP-B No. 2615200 and so forth.
It should, however, be noted that the use of such materials in the
present invention is not confined thereto.
[0130] The resin base material forms a layer in which the
low-molecular organic material is uniformly dispersed and held, and
the resin base material affects the transparency when the
thermoreversible recording medium becomes most transparent. For
this reason, the resin base material is preferably a resin which is
highly transparent, mechanically stable and excellent in
film-forming property.
[0131] Such a resin is not particularly limited and may be suitably
selected in accordance with the intended use. Examples thereof
include polyvinyl chloride; vinyl chloride copolymers such as vinyl
chloride-vinyl acetate copolymers, vinyl chloride-vinyl
acetate-vinyl alcohol copolymers, vinyl chloride-vinyl
acetate-maleic acid copolymers and vinyl chloride-acrylate
copolymers; polyvinylidene chloride; vinylidene chloride copolymers
such as vinylidene chloride-vinyl chloride copolymers and
vinylidene chloride-acrylonitrile copolymers; polyesters;
polyamides; polyacrylates, polymethacrylates and
acrylate-methacrylate copolymers; and silicone resins. Each of
these may be used alone or in combination with two or more.
[0132] The mass ratio of the low-molecular organic material to the
resin (resin base material) in the recording layer is preferably in
the range of approximately 2:1 to 1:16, more preferably in the
range of approximately 1:2 to 1:8.
[0133] When the amount of the resin contained is so small as to be
outside the mass ratio 2:1, it may be difficult to form a film in
which the low-molecular organic material is held in the resin base
material. When the amount of the resin contained is so large as to
be outside the mass ratio 1:16, the amount of the low-molecular
organic material is small, and thus it may be difficult to make the
recording layer opaque.
[0134] Besides the low-molecular organic material and the resin,
other components such as a high-boiling solvent and a surfactant
may be added into the recording layer for the purpose of making it
easier to record a transparent image.
[0135] The method for producing the recording layer is not
particularly limited and may be suitably selected in accordance
with the intended use. For instance, the recording layer can be
produced as follows: a solution dissolving the resin base material
and the low-molecular organic material, or a dispersion solution
produced by dispersing the low-molecular organic material in the
form of fine particles into a solution containing the resin base
material (a solvent contained herein does not dissolve at least one
selected from the above-mentioned low-molecular organic materials)
is applied onto the support and dried.
[0136] The solvent used for producing the recording layer is not
particularly limited and may be suitably selected according to the
types of the resin base material and the low-molecular organic
material. Examples of the solvent include tetrahydrofuran, methyl
ethyl ketone, methyl isobutyl ketone, chloroform, carbon
tetrachloride, ethanol, toluene and benzene. When the solution is
used, as well as when the dispersion solution is used, the
low-molecular organic material is deposited in the lo form of fine
particles and present in a dispersed state in the recording layer
obtained.
[0137] Composed of the leuco dye and the reversible developer, the
low-molecular organic material in the thermoreversible recoding
medium may develop color at a second specific temperature and lose
the color at a first specific temperature. The leuco dye is a dye
precursor which is colorless or pale per se. The leuco dye is not
particularly limited and may be suitably selected from known leuco
dyes. Examples thereof include leuco compounds based upon
triphenylmethane phthalide, triallylmethane, fluoran,
phenothiazine, thiofluoran, xanthene, indophthalyl, spiropyran,
azaphthalide, chromenopyrazole, methines, rhodamineanilinolactam,
rhodaminelactam, quinazoline, diazaxanthene and bislactone. Among
these, leuco dyes based upon fluoran and phthalide are particularly
preferable in that they are excellent in color-developing and
color-erasing property, colorfulness and storage ability. Each of
these may be used alone or in combination with two or more, and the
thermoreversible recording medium can be made suitable for
multicolor or full-color recording by providing a layer which
develops color with a different color tone.
[0138] The reversible developer is not particularly limited and may
be suitably selected in accordance with the intended use, as long
as it is capable of reversibly developing and erasing color by
means of heat. Suitable examples thereof include a compound having
in its molecules at least one of the following structures: a
structure (1) having such a color-developing ability as makes the
leuco dye develop color (for example, a phenolic hydroxyl group, a
carboxylic acid group, a phosphoric acid group, etc.); and a
structure (2) which controls cohesion among molecules (for example,
a structure in which long-chain hydrocarbon groups are linked
together). In the bonded site, the long-chain hydrocarbon group may
be bonded via a divalent or more bond group containing a hetero
atom. Additionally, the long-chain hydrocarbon groups may contain
at least either similar linking groups or aromatic groups.
[0139] For the structure (1) having such a color-developing ability
as makes the leuco dye develop color, phenol is particularly
suitable.
[0140] For the structure (2) which controls cohesion among
molecules, long-chain hydrocarbon groups having 8 or more carbon
atoms, preferably 11 or more carbon atoms, are suitable, and the
upper limit of the number of carbon atoms is preferably 40 or less,
more preferably 30 or less.
[0141] Among the reversible developers, phenolic compounds
represented by General Formula (1) are desirable, and phenolic
compounds represented by General Formula (2) are more
desirable.
##STR00001##
[0142] In General Formulae (1) and (2), R.sup.1 denotes a single
bond or an aliphatic hydrocarbon group having 1 to 24 carbon atoms.
R.sup.2 denotes an aliphatic hydrocarbon group having two or more
carbon atoms, which may have a substituent, and the number of the
carbon atoms is preferably 5 or greater, more preferably 10 or
greater. R.sup.3 denotes an aliphatic hydrocarbon group having 1 to
35 carbon atoms, and the number of the carbon atoms is preferably 6
to 35, more preferably 8 to 35. Each of these aliphatic hydrocarbon
groups may be provided alone or in combination with two or
more.
[0143] The sum of the numbers of carbon atoms which R.sup.1,
R.sup.2 and R.sup.3 have is not particularly limited and may be
suitably selected in accordance with the intended use, with its
lower limit being preferably 8 or greater, more preferably 11 or
greater, and its upper limit being preferably 40 or less, more
preferably 35 or less.
[0144] When the sum of the numbers of carbon atoms is less than 8,
color-developing stability or color-erasing ability may
degrade.
[0145] Each of the aliphatic hydrocarbon groups may be a
straight-chain group or a branched-chain group and may have an
unsaturated bond, with preference being given to a straight-chain
group. Examples of the substituent bonded to the aliphatic
hydrocarbon group include hydroxyl group, halogen atoms and alkoxy
groups.
[0146] X and Y may be identical or different, each denoting an N
atom-containing or O atom-containing divalent group. Specific
examples thereof include oxygen atom, amide group, urea group,
diacylhydrazine group, diamide oxalate group and acylurea group,
with amide group and urea group being preferable.
[0147] "n" denotes an integer of 0 to 1.
[0148] It is desirable that the electron-accepting compound
(developer) be used together with a compound as a color erasure
accelerator having in its molecules at least one of --NHCO-- group
and --OCONH-- group because intermolecular interaction is induced
between the color erasure accelerator and the developer in a
process of producing a colorless state and thus there is an
improvement in color-developing and color-erasing property.
[0149] For the reversible thermosensitive recording layer, a binder
resin and, if necessary, additives for improving or controlling the
coating properties and color-developing and color-erasing
properties of the recording layer may be used. Examples of these
additives include a surfactant, a conductive agent, a filling
agent, an antioxidant, a light stabilizer, a color development
stabilizer and a color erasure accelerator.
[0150] The binder resin is not particularly limited and may be
suitably selected in accordance with the intended use, as long as
it enables the recording layer to be bonded onto the support. For
instance, one of conventionally known resins or a combination of
two or more thereof may be used for the binder resin. Among these
resins, resins capable of being cured by heat, an ultraviolet ray,
an electron beam or the like are preferable in that the durability
at the time of repeated use can be improved, with particular
preference being given to thermosetting resins each containing an
isocyanate-based compound or the like as a cross-linking agent.
Examples of the thermosetting resins include a resin having a group
which reacts with a cross-linking agent, such as a hydroxyl group
or carboxyl group, and a resin produced by copolymerizing a
hydroxyl group-containing or carboxyl group-containing monomer and
other monomer. Specific examples of such thermosetting resins
include phenoxy resins, polyvinyl butyral resins, cellulose acetate
propionate resins, cellulose acetate butyrate resins, acrylpolyol
resins, polyester polyol resins and polyurethane polyol resins,
with particular preference being given to acrylpolyol resins,
polyester polyol resins and polyurethane polyol resins.
[0151] The mixture ratio (mass ratio) of the color developer to the
binder resin in the recording layer is preferably in the range of
1:0.1 to 1:10. When the amount of the binder resin is too small,
the recording layer may be deficient in thermal strength. When the
amount of the binder resin is too large, it is problematic because
the color-developing density decreases.
[0152] The cross-linking agent is not particularly limited and may
be suitably selected in accordance with the intended use, and
examples thereof include isocyanates, amino resins, phenol resins,
amines and epoxy compounds. Among these, isocyanates are
preferable, and polyisocyanate compounds each having a plurality of
isocyanate groups are particularly preferable.
[0153] As to the amount of the cross-linking agent added in
relation to the amount of the binder resin, the ratio of the number
of functional groups contained in the cross-linking agent to the
number of active groups contained in the binder resin is preferably
in the range of 0.01:1 to 2:1. When the amount of the cross-linking
agent added is so small as to be outside this range, sufficient
thermal strength cannot be obtained. When the amount of the
cross-linking agent added is so large as to be outside this range,
there is an adverse effect on the color-developing and
color-erasing properties.
[0154] Further, as a cross-linking promoter, a catalyst utilized in
this kind of reaction may be used.
[0155] The gel fraction of any of the thermosetting resins in the
case where thermally cross-linked is preferably 30% or greater,
more preferably 50% or greater, even more preferably 70% or
greater. When the gel fraction is less than 30%, an adequate
cross-linked state cannot be produced, and thus there may be
degradation of durability.
[0156] As to a method for distinguishing between a cross-linked
state and a non-cross-linked state of the binder resin, these two
states can be distinguished by immersing a coating film in a
solvent having high dissolving ability, for example. Specifically,
with respect to the binder resin in a non-cross-linked state, the
resin dissolves in the solvent and thus does not remain in a
solute.
[0157] The above-mentioned other components in the recording layer
are not particularly limited and may be suitably selected in
accordance with the intended use. For instance, a surfactant, a
plasticizer and the like are suitable therefor in that recording of
an image can be facilitated.
[0158] To a solvent, a coating solution dispersing device, a
recording layer applying method, a drying and hardening method and
the like used for the recording layer coating solution, those that
are known can be applied.
[0159] To prepare the recording layer coating solution, materials
may be together dispersed into a solvent using the dispersing
device; alternatively, the materials may be independently dispersed
into respective solvents and then the solutions may be mixed
together. Further, the ingredients may be heated and dissolved, and
then they may be precipitated by rapid cooling or slow cooling.
[0160] The method for forming the recording layer is not
particularly limited and may be suitably selected in accordance
with the intended use. Suitable examples thereof include a method
(1) of applying onto a support a recording layer coating solution
in which the resin, the electron-donating color-forming compound
and the electron-accepting compound are dissolved or dispersed in a
solvent, then cross-linking the coating solution while or after
forming it into a sheet or the like by evaporation of the solvent;
a method (2) of applying onto a support a recording layer coating
solution in which the electron-donating color-forming compound and
the electron-accepting compound are dispersed in a solvent
dissolving only the resin, then cross-linking the coating solution
while or after forming it into a sheet or the like by evaporation
of the solvent; and a method (3) of not using a solvent and heating
and melting the resin, the electron-donating color-forming compound
and the electron-accepting compound so as to mix, then
cross-linking this melted mixture after forming it into a sheet or
the like and cooling it. In each of these methods, it is also
possible to produce the recording layer as a thermoreversible
recording medium in the form of a sheet, without using the
support.
[0161] The solvent used in (1) or (2) cannot be unequivocally
defined, as it is affected by the types, etc. of the resin, the
electron-donating color-forming compound and the electron-accepting
compound. Examples thereof include tetrahydrofuran, methyl ethyl
ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride,
ethanol, toluene and benzene.
[0162] Additionally, the electron-accepting compound is present in
the recording layer, being dispersed in the form of particles.
[0163] Pigments, an antifoaming agent, a dispersant, a slip agent,
an antiseptic agent, a cross-linking agent, a plasticizer and the
like may be added into the recording layer coating solution, for
the purpose of exhibiting high performance as a coating
material.
[0164] The coating method for the recording layer is not
particularly limited and may be suitably selected in accordance
with the intended use. For instance, a support which is continuous
in the form of a roll or which has been cut into the form of a
sheet is conveyed, and the support is coated with the recording
layer by a known method such as blade coating, wire bar coating,
spray coating, air knife coating, bead coating, curtain coating,
gravure coating, kiss coating, reverse roll coating, dip coating or
die coating.
[0165] The drying conditions of the recording layer coating
solution are not particularly limited and may be suitably selected
in accordance with the intended use. For instance, the recording
layer coating solution is dried at room temperature to a
temperature of 140.degree. C., for approximately 10 sec to 10
min.
[0166] The thickness of the recording layer is not particularly
limited and may be suitably selected in accordance with the
intended use. For instance, it is preferably 1 .mu.m to 20 .mu.m,
more preferably 3 .mu.m to 15 .mu.m. When the recording layer is
too thin, the contrast of an image may lower because the
color-developing density lowers. When the recording layer is too
thick, the heat distribution in the layer increases, a portion
which does not reach a color-developing temperature and so does not
develop color is created, and thus a desired color-developing
density may be unable to be obtained.
--Photothermal Conversion Layer--
[0167] The photothermal conversion layer is a layer having a
function to absorb laser beams and generate heat and contains at
least a photothermal conversion material having a function to
absorb laser beams and generate heat.
[0168] The photothermal conversion material is broadly classified
into inorganic materials and organic materials.
[0169] Examples of the inorganic materials include carbon black,
metals such as Ge, Bi, In, Te, Se, and Cr, or semi-metals thereof
or alloys thereof. Each of these inorganic materials is formed into
a layer form by vacuum evaporation method or by bonding a
particulate material to a layer surface using a resin or the
like.
[0170] For the organic material, various dyes can be suitably used
in accordance with the wavelength of light to be absorbed, however,
when a laser diode is used as a light source, a near-infrared
absorption pigment having an absorption peak near wavelengths of
700 nm to 1,500 nm. Specific examples thereof include cyanine
pigments, quinone pigments, quinoline derivatives of indonaphthol,
phenylene diamine-based nickel complexes, phthalocyanine compounds,
and naphthalocyanine compounds. To secure durability against
repeated recording and erasure of an image, it is preferable to
select a photothermal conversion material that is excellent in heat
resistance.
[0171] Each of the photothermal conversion materials may be used
alone or in combination with two or more. The photothermal
conversion material may be mixed in the recording layer. In this
case, the recording layer also serves as the photothermal
conversion layer. Among these, in view of thermal durability
against repeated image recording and erasure and light resistance
of a medium, phthalocyanine pigment compounds are particularly
preferable, because of high stability against heat and light.
[0172] The amount of the photothermal conversion material in the
total mass of a layer containing the photothermal conversion
material is preferably 0.0005% by mass to 0.1% by mass, and more
preferably 0.001% by mass to 0.02% by mass. When the amount of the
photothermal conversion material is large, the background of a
thermoreversible recording medium is colored. When the amount is
small, a laser beam is less absorbed in a thermoreversible
recording medium, and sensitivity of image recording and erasure is
lowered.
[0173] When the photothermal conversion layer is formed, the
photothermal conversion material is typically used in combination
with a resin. The resin used in the photothermal conversion layer
is not particularly limited and may be suitably selected from among
those known in the art, as long as it can maintain the inorganic
material and the organic material therein, however, thermoplastic
resins and thermosetting resins are preferable.
[0174] To a solvent, a coating solution dispersing device, a
photothermal conversion layer applying method, a drying method and
the like used for a photothermal conversion layer, those that are
known and used for the recording layer can be applied.
[0175] The thickness of the photothermal conversion layer is not
particularly limited and may be suitably selected in accordance
with the intended use; it is preferably 0. 1 .mu.m to 10 .mu.m.
<Protective Layer>
[0176] In the thermoreversible recording medium of the present
invention, it is desirable that a protective layer be provided on
the recording layer, for the purpose of protecting the recording
layer. The protective layer is not particularly limited and may be
suitably selected in accordance with the intended use. For
instance, the protective layer may be formed from one or more
layers, and it is preferably provided on the outermost surface that
is exposed.
[0177] The protective layer contains a binder resin and further
contains other components such as a filler, a lubricant and a
coloring pigment in accordance with the necessity.
[0178] The resin in the protective layer is not particularly
limited and may be suitably selected in accordance with the
intended use. For instance, the resin is preferably a thermosetting
resin, an ultraviolet (UV) curable resin, an electron beam curable
resin, etc., with particular preference being given to an
ultraviolet (UV) curable resin and a thermosetting resin.
[0179] The UV-curable resin is capable of forming a very hard film
after cured, and reducing damage done by physical contact of the
surface and deformation of the medium caused by laser heating;
therefore, it is possible to obtain a thermoreversible recording
medium superior in durability against repeated use.
[0180] Although slightly inferior to the UV-curable resin, the
thermosetting resin makes it possible to harden the surface as well
and is superior in durability against repeated use.
[0181] The UV-curable resin is not particularly limited and may be
suitably selected from known UV-curable resins in accordance with
the intended use. Examples thereof include oligomers based upon
urethane acrylates, epoxy acrylates, polyester acrylates, polyether
acrylates, vinyls and unsaturated polyesters; and monomers such as
monofunctional and multifunctional acrylates, methacrylates, vinyl
esters, ethylene derivatives and allyl compounds. Among these,
multifunctional, i.e. tetrafunctional or higher, monomers and
oligomers are particularly preferable. By mixing two or more of
these monomers or oligomers, it is possible to suitably adjust the
hardness, degree of contraction, flexibility, coating strength,
etc. of the resin film.
[0182] To cure the monomers and the oligomers with an ultraviolet
ray, it is necessary to use a photopolymerization initiator or a
photopolymerization accelerator.
[0183] The amount of the photopolymerization initiator or the
photopolymerization accelerator added is preferably 0.1% by mass to
20% by mass, more preferably 1% by mass to 10% by mass, in relation
to the total mass of the resin component of the protective
layer.
[0184] Ultraviolet irradiation for curing the ultraviolet curable
resin can be conducted using a known ultraviolet irradiator, and
examples of the ultraviolet irradiator include one equipped with a
light source, lamp fittings, a power source, a cooling device, a
conveyance device, etc.
[0185] Examples of the light source include a mercury-vapor lamp, a
metal halide lamp, a potassium lamp, a mercury-xenon lamp and a
flash lamp. The wavelength of the light source may be suitably
selected according to the ultraviolet absorption wavelength of the
photopolymerization initiator and the photopolymerization
accelerator added to the thermoreversible recording medium
composition.
[0186] The conditions of the ultraviolet irradiation are not
particularly limited and may be suitably selected in accordance
with the intended use. For instance, it is advisable to decide the
lamp output, the conveyance speed, etc. according to the
irradiation energy necessary to cross-link the resin.
[0187] In order to improve the conveyance capability, a releasing
agent such as a silicone having a polymerizable group, a
silicone-grafted polymer, wax or zinc stearate; or a lubricant such
as silicone oil may be added. The amount of any of these added is
preferably 0.01% by mass to 50% by mass, more preferably 0.1% by
mass to 40% by mass, in relation to the total mass of the resin
component of the protective layer. Each of these may be used alone
or in combination with two or more. Additionally, in order to
prevent static electricity, a conductive filler is preferably used,
more preferably a needle-like conductive filler.
[0188] The particle diameter of the inorganic pigment is preferably
0.01 .mu.m to 10.0 .mu.m, more preferably 0.05 .mu.m to 8.0 .mu.m.
The amount of the inorganic pigment added is preferably 0.001 parts
by mass to 2 parts by mass, more preferably 0.005 parts by mass to
1 part by mass, in relation to 1 part by mass of the heat-resistant
resin.
[0189] Further, a surfactant, a leveling agent, an antistatic agent
and the like that are conventionally known may be contained in the
protective layer as additives.
[0190] Also, as the thermosetting resin, a resin similar to the
binder resin used for the recording layer can be suitably used, for
instance.
[0191] A polymer having an ultraviolet absorbing structure
(hereinafter otherwise referred to as "ultraviolet absorbing
polymer") may also be used.
[0192] Here, the polymer having an ultraviolet absorbing structure
denotes a polymer having an ultraviolet absorbing structure (e.g.
ultraviolet absorbing group) in its molecules. Examples of the
ultraviolet absorbing structure include salicylate structure,
cyanoacrylate structure, benzotriazole structure and benzophenone
structure. Among these, benzotriazole structure and benzophenone
structure are particularly preferable for their superior light
resistance.
[0193] It is desirable that the thermosetting resin be
cross-linked. Accordingly, the thermosetting resin is preferably a
resin having a group which reacts with a curing agent, such as
hydroxyl group, amino group or carboxyl group, particularly
preferably a hydroxyl group-containing polymer. To increase the
strength of a layer which contains the polymer having an
ultraviolet absorbing structure, use of the polymer having a
hydroxyl value of 10 mgKOH/g or greater is preferable because
adequate coating strength can be obtained, more preferably use of
the polymer having a hydroxyl value of 30 mgKOH/g or greater, even
more preferably use of the polymer having a hydroxyl value of 40
mgKOH/g or greater. By making the protective layer have adequate
coating strength, it is possible to reduce degradation of the
recording medium even when erasure and printing are repeatedly
carried out.
[0194] As the curing agent, a curing agent similar to the one used
for the recording layer can be suitably used.
[0195] To a solvent, a coating solution dispersing device, a
protective layer applying method, a drying method and the like used
for the protective layer coating solution, those that are known and
used for the recording layer can be applied. When an ultraviolet
curable resin is used, a curing step by means of the ultraviolet
irradiation with which coating and drying have been carried out is
required, in which case an ultraviolet irradiator, a light source
and the irradiation conditions are as described above.
[0196] The thickness of the protective layer is preferably 0.1
.mu.m to 20 .mu.m, more preferably 0.5 .mu.m to 10 .mu.m, even more
preferably 1.5 .mu.m to 6 .mu.m. When the thickness is less than
0.1 .mu.m, the protective layer cannot fully perform the function
as a protective layer of a thermoreversible recording medium, the
thermoreversible recording medium easily degrades through repeated
use with heat, and thus it may become unable to be repeatedly used.
When the thickness is greater than 20 .mu.m, it is impossible to
pass adequate heat to a thermosensitive section situated under the
protective layer, and thus printing and erasure of an image by heat
may become unable to be sufficiently performed.
<Intermediate Layer>
[0197] In the present invention, it is desirable to provide an
intermediate layer between the recording layer and the protective
layer, for the purpose of improving adhesiveness between the
recording layer and the protective layer, preventing change in the
quality of the recording layer caused by application of the
protective layer, and preventing the additives in the protective
layer from transferring to the recording layer. This makes it
possible to improve the ability to store a color-developing
image.
[0198] The intermediate layer contains at least a binder resin and
further contains other components such as a filler, a lubricant and
a coloring pigment in accordance with the necessity.
[0199] The binder resin is not particularly limited and may be
suitably selected in accordance with the intended use. For the
binder resin, the binder resin used for the recording layer or a
resin component such as a thermoplastic resin or thermosetting
resin may be used. Examples of the resin component include
polyethylene, polypropylene, polystyrene, polyvinyl alcohol,
polyvinyl butyral, polyurethane, saturated polyesters, unsaturated
polyesters, epoxy resins, phenol resins, polycarbonates and
polyamides.
[0200] It is desirable that the intermediate layer contain an
ultraviolet absorber. For the ultraviolet absorber, any one of an
organic compound and an inorganic compound may be used.
[0201] Also, an ultraviolet absorbing polymer may be used, and this
may be cured by means of a cross-linking agent. As these compounds,
compounds similar to those used for the protective layer can be
suitably used.
[0202] The thickness of the intermediate layer is preferably 0.1
.mu.m to 20 .mu.m, more preferably 0.5 .mu.m to 5 .mu.m. To a
solvent, a coating solution dispersing device, an intermediate
layer applying method, an intermediate layer drying and hardening
method and the like used for the intermediate layer coating
solution, those that are known and used for the recording layer can
be applied.
<Under Layer>
[0203] In the present invention, an under layer may be provided
between the recording layer and the support, for the purpose of
effectively utilizing applied heat for high sensitivity, or
improving adhesiveness between the support and the recording layer,
and preventing permeation of recording layer materials into the
support.
[0204] The under layer contains at least hollow particles, also
contains a binder resin and further contains other components in
accordance with the necessity.
[0205] Examples of the hollow particles include single hollow
particles in which only one hollow portion is present in each
particle, and multi hollow particles in which numerous hollow
portions are present in each particle. These types of hollow
particles may be used independently or in combination.
[0206] The material for the hollow particles is not particularly
limited and may be suitably selected in accordance with the
intended use, and suitable examples thereof include thermoplastic
resins. For the hollow particles, suitably produced hollow
particles may be used, or a commercially available product may be
used. Examples of the commercially available product include
MICROSPHERE R-300 (produced by Matsumoto Yushi-Seiyaku Co., Ltd.);
ROPAQUE HP 1055 and ROPAQUE HP433J (both of which are produced by
Zeon Corporation); and SX866 (Produced by JSR Corporation).
[0207] The amount of the hollow particles added into the under
layer is not particularly limited and may be suitably selected in
accordance with the intended use, and it is preferably 10% by mass
to 80% by mass, for instance.
[0208] For the binder resin, a resin similar to the resin used for
the recording layer or used for the layer which contains the
polymer having an ultraviolet absorbing structure can be used.
[0209] The under layer may contain at least one of an organic
filler and an inorganic filler such as calcium carbonate, magnesium
carbonate, titanium oxide, silicon oxide, aluminum hydroxide,
kaolin or talc.
[0210] Besides, the under layer may contain a lubricant, a
surfactant, a dispersant and so forth.
[0211] The thickness of the under layer is not particularly limited
and may be suitably selected in accordance with the intended use,
with the range of 0.1 .mu.m to 50 .mu.m being desirable, the range
of 2 .mu.m to 30 .mu.m being more desirable, and the range of 12
.mu.m to 24 .mu.m being even more desirable.
<Back Layer>
[0212] In the present invention, for the purpose of preventing curl
and static charge on the thermoreversible recording medium and
improving the conveyance capability, a back layer may be provided
on the side of the support opposite to the surface where the
recording layer is formed.
[0213] The back layer contains at least a binder resin and further
contains other components such as a filler, a conductive filler, a
lubricant and a coloring pigment in accordance with the
necessity.
[0214] The binder resin is not particularly limited and may be
suitably selected in accordance with the intended use. For
instance, the binder resin is any one of a thermosetting resin, an
ultraviolet (UV) curable resin, an electron beam curable resin,
etc., with particular preference being given to an ultraviolet (UV)
curable resin and a thermosetting resin.
[0215] For the ultraviolet curable resin, the thermosetting resin,
the filler, the conductive filler and the lubricant, ones similar
to those used for the recording layer, the protective layer or the
intermediate layer can be suitably used.
<Adhesion Layer or Tackiness Layer>
[0216] In the present invention, the thermoreversible recording
medium can be produced as a thermoreversible recording label by
providing an adhesion layer or a tackiness layer on the surface of
the support opposite to the surface where the recording layer is
formed. The material for the adhesion layer or the tackiness layer
can be selected from commonly used materials.
[0217] The material for the adhesion layer or the tackiness layer
is not particularly limited and may be suitably selected in
accordance with the intended use. Examples thereof include urea
resins, melamine resins, phenol resins, epoxy resins, vinyl acetate
resins, vinyl acetate-acrylic copolymers, ethylene-vinyl acetate
copolymers, acrylic resins, polyvinyl ether resins, vinyl
chloride-vinyl acetate copolymers, polystyrene resins, polyester
resins, polyurethane resins, polyamide resins, chlorinated
polyolefin resins, polyvinyl butyral resins, acrylic acid ester
copolymers, methacrylic acid ester copolymers, natural rubbers,
cyanoacrylate resins and silicone resins.
[0218] The material for the adhesion layer or the tackiness layer
may be of a hot-melt type. Release paper may or may not be used. By
thusly providing the adhesion layer or the tackiness layer, the
thermoreversible recording label can be affixed to a whole surface
or a part of a thick substrate such as a magnetic stripe-attached
vinyl chloride card, which is difficult to coat with a recording
layer. This makes it possible to improve the convenience of this
medium, for example to display part of information stored in a
magnetic recorder. The thermoreversible recording label provided
with such an adhesion layer or tackiness layer can also be used on
thick cards such as IC cards and optical cards.
[0219] In the thermoreversible recording medium, a colored layer
may be provided between the support and the recording layer, for
the purpose of improving visibility. The colored layer can be
formed by applying a dispersion solution or a solution containing a
colorant and a resin binder over a target surface and drying the
dispersion solution or the solution; alternatively, the colored
layer can be formed by simply bonding a colored sheet to the target
surface.
[0220] The thermoreversible recording medium may be provided with a
color printing layer. A colorant in the color printing layer is,
for example, selected from dyes, pigments and the like contained in
color inks used for conventional full-color printing. Examples of
the resin binder include thermoplastic resins, thermosetting
resins, ultraviolet curable resins and electron beam curable
resins. The thickness of the color printing layer may be suitably
selected according to the desired printed color density.
[0221] In the thermoreversible recording medium, an irreversible
recording layer may be additionally used. In this case, the
color-developing color tones of the recording layers may be
identical or different. Also, a colored layer which has been
printed in accordance with offset printing, gravure printing, etc.
or which has been printed with a pictorial design or the like using
an ink-jet printer, a thermal transfer printer, a sublimation
printer, etc., for example, may be provided on the whole or a part
of the same surface of the thermoreversible recording medium of the
present invention as the surface where the recording layer is
formed, or may be provided on a part of the opposite surface
thereof. Further, an OP varnish layer composed mainly of a curable
resin may be provided on a part or the whole surface of the colored
layer. Examples of the pictorial design include letters/characters,
patterns, diagrams, photographs, and information detected with an
infrared ray. Also, any of the layers that are simply formed may be
colored by addition of dye or pigment.
[0222] Further, the thermoreversible recording medium of the
present invention may be provided with a hologram for security.
Also, to give variety in design, it may also be provided with a
design such as a portrait, a company emblem or a symbol by forming
depressions and protrusions in relief or in intaglio.
[0223] The thermoreversible recording medium may be formed into a
desired shape according to its use, for example into a card, a tag,
a label, a sheet or a roll. The thermoreversible recording medium
in the form of a card can be used for prepaid cards, discount
cards, credit cards and the like. The thermoreversible recording
medium in the form of a tag that is smaller in size than the card
can be used for price tags and the like. The thermoreversible
recording medium in the form of a tag that is larger in size than
the card can be used for tickets, sheets of instruction for process
control and shipping, and the like. The thermoreversible recording
medium in the form of a label can be affixed; accordingly, it can
be formed into a variety of sizes and, for example, used for
process control and product control, being affixed to carts,
receptacles, boxes, containers, etc. to be repeatedly used. The
thermoreversible recording medium in the form of a sheet that is
larger in size than the card offers a larger area for printing, and
thus it can be used for general documents and sheets of instruction
for process control, for example.
<Example of Combination of Thermoreversible Recording Member and
RF-ID>
[0224] A thermoreversible recording member used in the present
invention is superior in convenience because the recording layer
capable of reversible display, and an information storage section
are provided on the same card or tag (so as to form a single unit),
and part of information stored in the information storage section
is displayed on the recording layer, thereby making it is possible
to confirm the information by simply looking at a card or a tag
without needing a special device. Also, when information stored in
the information storage section is rewritten, rewriting of
information displayed by the thermoreversible recording member
makes it possible to use the thermoreversible recording medium
repeatedly as many times as desired.
[0225] The information storage section is not particularly limited
and may be suitably selected in accordance with the intended use,
and suitable examples thereof include a magnetic recording layer, a
magnetic stripe, an IC memory, an optical memory and an RF-ID tag.
In the case where the information storage section is used for
process control, product control, etc., an RF-ID tag is
particularly preferable. The RF-ID tag is composed of an IC chip,
and an antenna connected to the IC chip.
[0226] The thermoreversible recording member includes the recording
layer capable of reversible display, and the information storage
section. Suitable examples of the information storage section
include an RF-ID tag.
[0227] Here, FIG. 6 shows a schematic diagram of an example of an
RF-ID tag 85. This RF-ID tag 85 is composed of an IC chip 81, and
an antenna 82 connected to the IC chip 81. The IC chip 81 is
divided into four sections, i.e. a storage section, a power
adjusting section, a transmitting section and a receiving section,
and communication is conducted as they perform their operations
allotted. As for the communication, the RF-ID tag communicates with
an antenna of a reader/writer by means of a radio wave so as to
transfer data. Specifically, there are such two methods as follows:
an electromagnetic induction method in which the antenna of the
RF-ID tag receives a radio wave from the reader/writer, and
electromotive force is generated by electromagnetic induction
caused by resonance; and a radio wave method in which electromotive
force is generated by a radiated electromagnetic field. In both
methods, the IC chip inside the RF-ID tag is activated by an
electromagnetic field from outside, information inside the chip is
converted to a signal, then the signal is emitted from the RF-ID
tag. This information is received by the antenna on the
reader/writer side and recognized by a data processing unit, then
data processing is carried out on the software side.
[0228] The RF-ID tag is formed into a label or a card and can be
affixed to the thermoreversible recording medium. The RF-ID tag may
be affixed to the recording layer surface or the back layer
surface, desirably to the back surface layer. To stick the RF-ID
tag and the thermoreversible recording medium together, a known
adhesive or tackiness agent may be used.
[0229] Additionally, the thermoreversible recording medium and the
RF-ID tag may be integrally formed by lamination or the like and
then formed into a card or a tag.
(Image Processing Apparatus)
[0230] An image processing apparatus of the present invention is
used in the image processing method of the present invention and
includes at least a laser beam emitting unit, a beam scanning unit
and a beam condensing unit, and an irradiation intensity
distribution adjusting unit, and further includes a cooling unit
and may include other members suitably selected in accordance with
the necessity.
--Laser Beam Emitting Unit--
[0231] For the laser beam emitting unit, a semiconductor laser
device is used.
[0232] The emission wavelength of a laser beam from the
semiconductor laser is a wavelength of a beam which can be emitted
from a semiconductor laser diode, and is a wavelength in the near
infrared range, i.e. preferably 0.70 .mu.m to 1.55 .mu.m, and more
preferably 0.8 .mu.m to 1.0 .mu.m.
[0233] When the laser beam having the above-mentioned wavelength is
used, the thermoreversible recording medium absorbs the laser beam
having the above-mentioned wavelength. Thus, it preferably has a
layer for absorbing the semiconductor laser beam, such as a
photothermal conversion layer or a recording layer in which
photothermal conversion material is added.
--Beam Scanning Unit--
[0234] The beam scanning unit is disposed on a surface from which a
laser beam is emitted in the laser beam emitting unit. Examples of
the laser beam scanning unit include a laser beam scanning unit
with the use of a galvano mirror, and a unit of moving a XY stage
on which a thermoreversible recording medium is fixed. The unit of
moving the XY stage is difficult to scan fine letters/characters at
high speed. Therefore, the laser beam scanning unit with the use of
a galvano mirror is preferably used as the scanning method.
--Beam Condensing Unit--
[0235] The beam condensing unit is a unit configured to condense a
laser beam on the thermoreversible recording medium. When a galvano
mirror is used, the distance from the beam condensing unit changes
in accordance with the scanning position on the thermoreversible
recording medium. Thus, a diameter of the condensed beam is changed
by using a normal convex lens in combination with the galvano
mirror. By contrast, as the beam condensing unit, an f.theta. lens
is used combination with the galvano mirror, so that the diameter
of the condensed beam can be kept constant regardless of the
scanning position on the thermoreversible recording medium.
--Irradiation Intensity Distribution Adjusting Unit--
[0236] The irradiation intensity distribution adjusting unit has a
function of changing the irradiation intensity distribution of the
laser beam.
[0237] The arrangement of the irradiation intensity distribution
adjusting unit is not particularly limited as long as it is
disposed on a surface from which a laser beam is emitted in the
laser beam emitting unit; the distance, etc. between the
irradiation intensity distribution adjusting unit and the laser
beam emitting unit may be suitably selected in accordance with the
intended use, and the irradiation intensity distribution adjusting
unit is preferably placed between the laser beam emitting unit and
the after-mentioned galvano mirror, more preferably between the
after-mentioned beam expander and the galvano mirror.
[0238] The irradiation intensity distribution adjusting unit has
the function of changing the irradiation intensity distribution
such that the ratio (I.sub.1/I.sub.2) of the irradiation intensity
(I.sub.1) of the applied laser beam in a central position of the
applied laser beam to the irradiation intensity (I.sub.2) of the
applied laser beam on a plane corresponding to 95% of the total
irradiation energy of the applied laser beam satisfies
1.20.ltoreq.I.sub.1/I.sub.2.ltoreq.1.29. Therefore, it is possible
to reduce degradation of the thermoreversible recording medium
caused by repeated image recording and erasure and to improve
durability against repeated use, with the image contrast being
maintained.
[0239] The irradiation intensity distribution adjusting unit is not
particularly limited and may be suitably selected in accordance
with the intended use. Suitable examples thereof include lenses,
filters, masks, mirrors and fiber couplings, with lenses being
preferable because of causing less energy loss, specifically
kaleidoscopes, integrators, beam homogenizers, aspheric beam
shapers (each of which is a combination of an intensity
transformation lens and a phase correction lens), aspheric element
lenses, and diffractive optical elements. When a filter, a mask or
the like is used, the irradiation intensity can be adjusted by
physically cutting a central part of the laser beam. Meanwhile,
when a mirror is used, the irradiation intensity can be adjusted by
using, for example, a deformable mirror that is linked to a
computer and can be mechanically changed in shape, or a mirror in
which the reflectance or the formation of depressions and
protrusions on the surface varies from part to part.
[0240] Among these, aspheric element lenses and diffractive optical
elements are particularly preferable, because of high degree of
design flexibility in the intensity distribution adjusting element.
A semiconductor laser having emission wavelengths of visible light
to near infrared light is preferably used, because the irradiation
intensity of the applied laser beam is easily adjusted by fiber
coupling.
--Cooling Unit--
[0241] As the cooling unit configured to cool a semiconductor laser
diode while measuring and controlling the temperature thereof,
air-cooling, water-cooling or the like are used. Water-cooling is
efficient, but it leads to an increase in the size of a device.
Generally, air-cooling is used in a semiconductor laser having a
low output of 50 W or less, and water-cooling is used in a
semiconductor laser having an output of 50 W or more.
[0242] The semiconductor laser diode is necessary to be cooled,
because the temperature thereof increases due to continuous beam
emission, and diode itself may be broken. Moreover, an output of
the laser beam and an emission wavelength may change in accordance
with the temperature of the semiconductor laser diode. Thus, the
semiconductor laser device can obtain stable irradiation output by
providing the cooling unit so as to measure the temperature of the
semiconductor laser diode and to keep the temperature constant.
[0243] The basic configuration of the image processing apparatus of
the present invention is similar to that of a so-called laser
maker, except that it has at least a laser beam emission unit, the
beam scanning unit, the beam condensing unit and the irradiation
intensity distribution adjusting unit. The image processing
apparatus of the present invention includes at least an oscillator
unit, a power control unit, and a program unit.
[0244] Here, in FIG. 3 an example of the image processing apparatus
of the present invention, specifically a laser irradiation unit is
illustrated.
[0245] The image processing apparatus shown in FIG. 3 uses a fiber
coupled semiconductor laser (LIMO25F100-DL808-EX362, produced by
LIMO Lissotschenko Mikrooptik GmbH) having an emission wavelength
of 808 nm, a fiber diameter of 100 .mu.m and a maximum output of 25
W, as a laser source. A laser beam is emitted from a fiber 1, and
immediately after the laser emission, the laser beam is collimated
by a collimator 2. In parallel optical paths, an aspheric element
lens shown in FIG. 7 combined with the fiber is used as the
irradiation intensity distribution adjusting unit, and a distance
between an f.theta. lens 6 and a thermoreversible recording medium
7 is adjusted so as to change the ratio (I.sub.1/I.sub.2) of the
irradiation intensity (I.sub.1) of the applied laser beam in a
central position of the applied laser beam to the irradiation
intensity (I.sub.2) of the applied laser beam on a plane
corresponding to 95% of the total irradiation energy of the applied
laser beam.
[0246] The oscillator unit consists of a semiconductor laser diode
10, the collimator 2, a scanning unit 5 and the like.
[0247] The scanning unit 5 is composed of two galvanometers
containing mirrors 4 (not shown). By subjecting the laser beam,
which has been output from the semiconductor laser diode 10, to
high-speed rotary scanning, utilizing two mirrors 4 for the X axis
and Y axis directions attached to the galvanometers, an image is
recorded onto or erased from a thermoreversible recording medium
7.
[0248] In FIG. 3, 1, 3 and 8 respectively denote a fiber, mirror
and lens.
[0249] The power control unit is composed of a power source for
electric discharge; a power source for driving the galvanometer; a
power source for cooling a Peltier device, etc.; a control unit for
controlling the overall image processing apparatus; and the
like.
[0250] The program unit consists of a computer for controlling, in
which a software is installed, and is configured to input
conditions such as the intensity of the laser beam and the speed of
the laser scanning for recording or erasure of an image, and to
produce and edit letters/characters, etc. to be recorded in
accordance with a command from the software.
[0251] The laser irradiation unit, that is, a head part for an
image recording/erasure is mounted in the image processing
apparatus. In addition, the image processing apparatus includes a
part of conveying the thermoreversible recording medium and a
control part thereof, a monitor and the like.
[0252] The image processing method and the image processing
apparatus of the present invention are capable of repeatedly
recording and erasing a high-contrast image at high speed and in a
noncontact manner onto and from a thermoreversible recording
medium, for example a label affixed to cardboard or to a receptacle
such as a plastic container, and also capable of reducing
degradation of the thermoreversible recording medium caused by
repeated use. Hence, they can be particularly suitably used in
product distribution and delivery systems. In this case, for
instance, it is possible to record and erase an image onto and from
the label while moving the cardboard or the plastic container
placed on a conveyor belt, and to shorten the shipping time because
the line does not need stopping. Also, the cardboard or the plastic
container to which the label is affixed can be reused as it is,
without the need to detach the label, and subjected to image
erasure and recording again.
[0253] According to the present invention, it is possible to solve
conventional problems and to provide an image processing method and
an image processing apparatus, wherein a thermoreversible recording
medium can be uniformly heated, excessive energy is not applied to
the thermoreversible recording medium, degradation of the
thermoreversible recording medium can be reduced when recording and
erasure are repeatedly carried out, durability against repeated use
can be improved, and written lines can be changed in width by
adjusting the irradiation power, without needing to change the
irradiation distance.
EXAMPLES
[0254] Hereinafter, Examples of the present invention will be
explained. However, it should be noted that the present invention
is not confined to these Examples in any way.
Production Example 1
<Production of Thermoreversible Recording Medium>
[0255] A thermoreversible recording medium in which color tone
changed reversibly (transparent state--color-developed state)
depending upon temperature was produced in the following
manner.
--Support--
[0256] As a support, a white turbid polyester film (TETORON FILM
U2L98 W, produced by Teijin DuPont Films Japan Limited) having a
thickness of 125 .mu.m was used.
--Under Layer--
[0257] Thirty (30) parts by mass of a styrene-butadiene copolymer
(PA-9159, produced by Nippon A&L Inc.), 12 parts by mass of a
polyvinyl alcohol resin (POVAL PVA103, produced by Kuraray Co.,
Ltd.), 20 parts by mass of hollow particles (MICROSPHERE R-300,
produced by Matsumoto Yushi-Seiyaku Co., Ltd.) and 40 parts by mass
of water were mixed, and stirred for approximately 1 hr so as to be
uniformly mixed, thereby preparing an under layer coating
solution.
[0258] Next, an under layer having a thickness of 20 .mu.m was
formed by applying the obtained under layer coating solution onto
the support with the use of a wire bar, then heating and drying the
under layer coating solution at 80.degree. C. for 2 min.
--Thermoreversible Recording Layer (Recording Layer)--
[0259] Using a ball mill, 5 parts by mass of the reversible
developer represented by Structural Formula (1) below, 0.5 parts by
mass each of the two types of color erasure accelerators
represented by Structural Formulae (2) and (3) below, 10 parts by
mass of a 50% acrylpolyol solution (hydroxyl value=200 mgKOH/g),
and 80 parts by mass of methyl ethyl ketone were pulverized and
dispersed such that the average particle diameter became
approximately 1 .mu.m.
##STR00002##
[0260] Next, into the dispersion solution in which the reversible
developer had been pulverized and dispersed, 1 part by mass of
2-anilino-3-methyl-6-dibutylaminofluoran as a leuco dye, 0.2 parts
by mass of the phenolic antioxidant (IRGANOX 565, produced by Ciba
Specialty Chemicals plc.) represented by Structural Formula (4)
below, and 5 parts by mass of an isocyanate (CORONATE HL, produced
by Nippon Polyurethane Industry Co., Ltd.) were added. In the
obtained solution, 0.02% by mass of a photothermal conversion
material (IR14, a phthalocyanine compound produced by NIPPON
SHOKUBAI CO., LTD.) was added, and then sufficiently stirred to
prepare a recording layer coating solution.
##STR00003##
[0261] Subsequently, the prepared recording layer coating solution
was applied, using a wire bar, onto the support over which the
under layer had already been formed, and the recording layer
coating solution was dried at 100.degree. C. for 2 min, then cured
at 60.degree. C. for 24 hr so as to form a recording layer having a
thickness of 11 .mu.m.
--Intermediate Layer--
[0262] Three (3) parts by mass of a 50% acrylpolyol resin solution
(LR327, produced by Mitsubishi Rayon Co., Ltd.), 7 parts by mass of
a 30% zinc oxide fine particle dispersion solution (ZS303, produced
by Sumitomo Cement Co., Ltd.), 1.5 parts by mass of an isocyanate
(CORONATE HL, produced by Nippon Polyurethane Industry Co., Ltd.),
and 7 parts by mass of methyl ethyl ketone were mixed, and
sufficiently stirred to prepare an intermediate layer coating
solution.
[0263] Next, the intermediate layer coating solution was applied,
using a wire bar, onto the support over which the under layer and
the recording layer had already been formed, and the intermediate
layer coating solution was heated and dried at 90.degree. C. for 1
min, and then heated at 60.degree. C. for 2 hr so as to form an
intermediate layer having a thickness of 2 .mu.m.
--Protective Layer--
[0264] Three (3) parts by mass of pentaerythritol hexaacrylate
(KAYARAD DPHA, produced by Nippon Kayaku Co., Ltd.), 3 parts by
mass of an urethane acrylate oligomer (ART RESIN UN-3320HA,
produced by Negami Chemical Industrial Co., Ltd.), 3 parts by mass
of an acrylic acid ester of dipentaerythritol caprolactone (KAYARAD
DPCA-120, produced by Nippon Kayaku Co., Ltd.), 1 part by mass of a
silica (P-526, produced by Mizusawa Industrial Chemicals, Ltd.),
0.5 parts by mass of a photopolymerization initiator (IRGACURE 184,
produced by Nihon Ciba-Geigy K.K.), and 11 parts by mass of
isopropyl alcohol were mixed, and sufficiently stirred and
dispersed by the use of a ball mill, such that the average particle
diameter became approximately 3 .mu.m, thereby preparing a
protective layer coating solution.
[0265] Next, the protective layer coating solution was applied,
using a wire bar, onto the support over which the under layer, the
recording layer and the intermediate layer had already been formed,
and the protective layer coating solution was heated and dried at
90.degree. C. for 1 min, then cross-linked by means of an
ultraviolet lamp of 80 W/cm, so as to form a protective layer
having a thickness of 4 .mu.m.
--Back Layer--
[0266] Pentaerythritol hexaacrylate (KAYARAD DPHA, produced by
Nippon Kayaku Co., Ltd.)(7.5 parts by mass), 2.5 parts by mass of
an urethane acrylate oligomer (ART RESIN UN-3320HA, produced by
Negami Chemical Industrial Co., Ltd.), 2.5 parts by mass of a
needle-like conductive titanium oxide (FT-3000, major axis=5.15
.mu.m, minor axis=0.27 .mu.m, structure: titanium oxide coated with
antimony-doped tin oxide; produced by Ishihara Sangyo Kaisha,
Ltd.), 0.5 parts by mass of a photopolymerization initiator
(IRGACURE 184, produced by Nihon Ciba-Geigy K.K.) and 13 parts by
mass of isopropyl alcohol were mixed, and sufficiently stirred by
the use of a ball mill, so as to prepare a back layer coating
solution.
[0267] Next, the back layer coating solution was applied, using a
wire bar, onto the surface of the support opposite to the surface
thereof over which the recording layer, the intermediate layer and
the protective layer had already been formed, and the back layer
coating solution was heated and dried at 90.degree. C. for 1 min,
then cross-linked by means of an ultraviolet lamp of 80 W/cm, so as
to form a back layer having a thickness of 4 .mu.m. Thus, a
thermoreversible recording medium of Production Example 1 was
produced.
Production Example 2
<Production of Thermoreversible Recording Medium>
[0268] A thermoreversible recording medium in which transparency
changed reversibly (transparent state--white turbid state)
depending upon temperature was produced in the following
manner.
--Support--
[0269] As a support, a transparent PET film (LUMIRROR 175-T12,
produced by Toray Industries, Inc.) having a thickness of 175 .mu.m
was used.
--Thermoreversible Recording Layer (Recording Layer)--
[0270] Into a resin-containing solution in which 26 parts by mass
of a vinyl chloride copolymer (M 110, produced by ZEON CORPORATION)
was dissolved in 210 parts by mass of methyl ethyl ketone, 3 parts
by mass of the low-molecular organic material represented by
Structural Formula (5) below and 7 parts by mass of docosyl
behenate were added, and then, in a glass jar, ceramic beads having
a diameter of 2 mm were set, and the mixture was dispersed for 48
hr using PAINT SHAKER (produced by Asada Iron Works. Co., Ltd), so
as to prepare a uniformly dispersed solution.
##STR00004##
[0271] Next, in the obtained dispersion solution, 4 parts by mass
of an isocyanate compound (CORONATE 2298-90T, produced by Nippon
Polyurethane Industry Co., Ltd.) was added. In this solution, 0.02%
by mass of a photothermal conversion material (IR14, a
phthalocyanine compound produced by NIPPON SHOKUBAI CO., LTD.) was
added, and then sufficiently stirred to prepare a recording layer
coating solution.
[0272] Subsequently, the obtained recording layer solution was
applied on the support, then heated and dried; thereafter, the
recording layer solution was stored at 65.degree. C. for 24 hr; so
as to cross-link the resin. Thus, a thermosensitive recording layer
having a thickness of 10 .mu.m was provided over the support.
--Protective Layer--
[0273] A solution containing 10 parts by mass of a 75% butyl
acetate solution of urethane acrylate ultraviolet curable resin
(UNIDIC C7-157, produced by Dainippon Ink and Chemicals,
Incorporated) and 10 parts by mass of isopropyl alcohol was
applied, using a wire bar, onto the thermosensitive recording
layer, then heated and dried; thereafter, the solution was cured by
ultraviolet irradiation with a high-pressure mercury-vapor lamp of
80 W/cm, so as to form a protective layer having a thickness of 3
.mu.m. Thus, a thermoreversible recording medium of Production
Example 2 was produced.
<Measurement of Laser Beam Intensity Distribution>
[0274] The intensity distribution of a laser beam was measured in
accordance with the following procedure.
[0275] First of all, a high-power laser beam analyzer (SCORPION
SCOR-20SCM produced by Point Grey Research Inc.) was set such that
the irradiation distance became the same as that at the time of
recording onto a thermoreversible recording medium, then darkening
was conducted using a beam splitter (BEAMSTAR-FX-BEAM SPLITTER
produced by OPHIR, in which a transparent mirror and a filter were
combined such that the laser output became 3.times.10.sup.-6, and
the laser beam intensity was measured with the high-power laser
beam analyzer. Next, the obtained laser beam intensity was formed
into a three-dimensional graph, and the intensity distribution of
the laser beam was thus obtained.
<Measurement of Reflection Density>
[0276] As to the measurement of the reflection density, a gray
scale (produced by Kodak Japan Ltd.) was scanned by a scanner
(CANOSCAN 4400, produced by Canon Inc.), the obtained digital
gray-scale values were correlated with density values measured by a
reflection densitometer (RD-914, produced by Macbeth Co.), and the
digital gray-scale values, obtained by scanning a recorded image
and an erased portion with the scanner, were converted to the
density values, which were defined as the reflection density
values.
[0277] In the present invention, erasure of an image was enabled
when the density of the erased portion was 1.5 or greater in the
case of a thermoreversible recording medium in which the
thermoreversible recording layer contained a resin and a
low-molecular organic material, and when the density of the erased
portion was 0.15 or less in the case of a thermoreversible
recording medium in which the thermoreversible recording layer
contained a leuco dye and a reversible developer. Additionally, as
to the thermoreversible recording medium in which the
thermoreversible recording layer contained a resin and a
low-molecular organic material, the density was measured, with a
sheet of black paper (O.D. value=1.7) being laid on the back
surface thereof.
Example 1
[0278] A semiconductor laser device equipped with a fiber-coupled
semiconductor laser having an output of 25 W and an emission
wavelength of 808 nm, in which the fiber was used as the
irradiation intensity distribution adjusting unit, was used as a
light source of a semiconductor laser as shown in FIG. 3, and an
image was recorded onto the thermoreversible recording medium of
Production Example 1 by applying a laser beam, as the laser output,
the irradiation distance, the focal distance of the f.theta. lens,
the spot diameter and the scanning speed were adjusted to 9.0 W,
155 mm, 150 mm, 0.72 mm and 1,000 mm/s, respectively.
[0279] On this occasion, the irradiation intensity (I.sub.1) of the
applied laser beam in a central position of the applied laser beam
was 1.29 times the irradiation intensity (I.sub.2) of the applied
laser beam on a plane corresponding to 95% of the total irradiation
energy of the applied laser beam. The temperature of the
semiconductor laser was controlled to maintain at 25.degree. C. by
air-cooling.
[0280] As for measurement of the line width on this occasion, the
line width was defined as the width of a line when the density
values were 0.5 or greater in the case where a gray scale (produced
by Kodak Japan Ltd.) was scanned by a scanner (CANOSCAN 4400,
produced by Canon Inc.), the obtained digital gray-scale values
were correlated with density values measured by a reflection
densitometer (RD-914, produced by Macbeth Co.), and the digital
gray-scale values, obtained by scanning a recorded image with the
scanner, were converted to the density values; and the line width
was calculated from a predetermined number of pixels (1,200 dpi)
for the digital gray-scale values. Thus, the line width was 0.33
mm.
[0281] Next, the laser output, the irradiation distance, the spot
diameter and the scanning speed were adjusted to 20 W, 195 mm, 3 mm
and 1,000 mm/s, respectively, and a laser beam was linearly scanned
across the recorded image at intervals of 0.59 mm so as to erase
the image. The density of the erased portion at that time was
0.15.
[0282] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 50 times, it turned out that image
erasure was possible with a density of 0.17 at the time when
repeated 250 times, and that an unerased portion was left with a
density of 0.20 at the time when repeated 300 times. When the
thermoreversible recording medium of Production Example 1 is used
in a product distribution and delivery system such as home
delivery, being affixed to a plastic container, the plastic
container is used with a one-week cycle in many cases, and so image
recording and image erasure are carried out once a week; meanwhile,
the plastic container is discarded in roughly three years in many
cases because of damage, dirt, etc.; thus, the thermoreversible
recording medium can keep being used during the lifetime of the
plastic container, without the need to replace it, as long as it
allows image recording and image erasure to be repeated 250
times.
[0283] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.20 mm. The results are shown in Table 1.
Example 2
[0284] The same semiconductor laser device as the one in Example 1
was used, and an image was recorded onto the thermoreversible
recording medium of Production Example 1 by applying a laser beam,
as the laser output, the irradiation distance, the spot diameter
and the scanning speed were adjusted to 9.2 W, 152 mm, 0.73 mm and
1,000 mm/s, respectively. On this occasion, the irradiation
intensity (I.sub.1) of the applied laser beam in a central position
of the applied laser beam was 1.25 times the irradiation intensity
(I.sub.2) of the applied laser beam on a plane corresponding to 95%
of the total irradiation energy of the applied laser beam. The line
width, which was measured similarly to that in Example 1, was 0.33
mm.
[0285] Next, the laser output, the irradiation distance, the spot
diameter and the scanning speed were adjusted to 20 W, 195 mm, 3 mm
and 1000 mm/s, respectively, and a laser beam was linearly scanned
across the recorded image at intervals of 0.59 mm so as to erase
the image. The density of the erased portion at that time was
0.15.
[0286] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 50 times, it turned out that image
erasure was possible with a density of 0.17 at the time when
repeated 400 times, and that an unerased portion was left with a
density of 0.20 at the time when repeated 450 times.
[0287] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.21 mm. The results are shown in Table 1.
Example 3
[0288] The same semiconductor laser device as the one in Example 1
was used, and an image was recorded onto the thermoreversible
recording medium of Production Example 1 by applying a laser beam,
as the laser output, the irradiation distance, the spot diameter
and the scanning speed were adjusted to 9.3 W, 150 mm, 0.75 mm and
1,000 mm/s, respectively. The irradiation intensity (I.sub.1) of
the applied laser beam in a central position of the applied laser
beam was 1.20 times the irradiation intensity (I.sub.2) of the
applied laser beam on a plane corresponding to 95% of the total
irradiation energy of the applied laser beam. The line width, which
was measured similarly to that in Example 1, was 0.33 mm.
[0289] Next, the laser output, the irradiation distance, the spot
diameter and the scanning speed were adjusted to 20 W, 195 mm, 3 mm
and 1,000 mm/s, respectively, and a laser beam was linearly scanned
across the recorded image at intervals of 0.59 mm so as to erase
the image. The density of the erased portion at that time was
0.15.
[0290] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 50 times, it turned out that image
erasure was possible with a density of 0.17 at the time when
repeated 600 times, and that an unerased portion was left with a
density of 0.20 at the time when repeated 650 times.
[0291] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.25 mm. The results are shown in Table 1.
Example 4
[0292] Image recording and image erasure were carried out similarly
to those in Example 1, except that the thermoreversible recording
medium of Production Example 1 was changed to the thermoreversible
recording medium of Production Example 2, the laser output at the
time of image recording was changed to 6.2 W, and the laser output
at the time of image erasure was changed to 14 W. The irradiation
intensity (I.sub.1) of the applied laser beam in a central position
of the applied laser beam was 1.29 times the irradiation intensity
(I.sub.2) of the applied laser beam on a plane corresponding to 95%
of the total irradiation energy of the applied laser beam. As for
measurement of the line width on this occasion, the line width was
defined as the width of a line when the density values were 1.15 or
less in the case where a gray scale (produced by Kodak Japan Ltd.)
was scanned by a scanner (CANOSCAN 4400, produced by Canon Inc.),
the obtained digital gray-scale values were correlated with density
values measured by a reflection densitometer (RD-914, produced by
Macbeth Co.), and the digital gray-scale values, obtained by
scanning a recorded image with the scanner, were converted to the
density values; and the line width was calculated from a
predetermined number of pixels (1,200dpi) for the digital
gray-scale values. Thus, the line width was 0.33 mm.
[0293] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 50 times, it turned out that image
erasure was possible with a density of 1.65 at the time when
repeated 400 times, and that an unerased portion was left with a
density of 1.51 at the time when repeated 450 times.
[0294] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.21 mm. The results are shown in Table 1.
Example 5
[0295] Image recording and image erasure were carried out similarly
to those in Example 2, except that the thermoreversible recording
medium of Production Example 1 was changed to the thermoreversible
recording medium of Production Example 2, the laser output at the
time of image recording was changed to 6.4 W, and the laser output
at the time of image erasure was changed to 14 W. The irradiation
intensity (I.sub.1) of the applied laser beam in a central position
of the applied laser beam was 1.25 times the irradiation intensity
(I.sub.2) of the applied laser beam on a plane corresponding to 95%
of the total irradiation energy of the applied laser beam. The line
width, which was measured similarly to that in Example 4, was 0.33
mm.
[0296] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 50 times, it turned out that image
erasure was possible with a density of 1.65 at the time when
repeated 600 times, and that an unerased portion was left with a
density of 1.52 at the time when repeated 650 times.
[0297] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.22 mm. The results are shown in Table 1.
Example 6
[0298] Image recording and image erasure were carried out similarly
to those in Example 3, except that the thermoreversible recording
medium of Production Example 1 was changed to the thermoreversible
recording medium of Production Example 2, the laser output at the
time of image recording was changed to 6.5 W, and the laser output
at the time of image erasure was changed to 14 W. The irradiation
intensity (I.sub.1) of the applied laser beam in a central position
of the applied laser beam was 1.20 times the irradiation intensity
(I.sub.2) of the applied laser beam on a plane corresponding to 95%
of the total irradiation energy of the applied laser beam. The line
width, which was measured similarly to that in Example 4, was 0.33
mm.
[0299] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 50 times, it turned out that image
erasure was possible with a density of 1.64 at the time when
repeated 800 times, and that an unerased portion was left with a
density of 1.50 at the time when repeated 850 times.
[0300] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.25 mm. The results are shown in Table 1.
Example 7
[0301] A semiconductor laser device equipped with a fiber coupled
semiconductor laser having an output of 25 W and an emission
wavelength of 808 nm, in which an aspheric element lens was
incorporated in the optical path, was used as a light source of a
semiconductor laser as shown in FIG. 3, and an image was recorded
onto the thermoreversible recording medium of Production Example 1
by applying a laser beam, as the laser output, the irradiation
distance, the focal distance of the f.theta. lens, the spot
diameter and the scanning speed were adjusted to 13.0 W, 155 mm,
150 mm, 0.92 mm and 1,000 mm/s, respectively. On this occasion, the
irradiation intensity (I.sub.1) of the applied laser beam in a
central position of the applied laser beam was 1.25 times the
irradiation intensity (I.sub.2) of the applied laser beam on a
plane corresponding to 95% of the total irradiation energy of the
applied laser beam.
[0302] As for measurement of the line width on this occasion, the
line width was defined as the width of a line when the density
values were 0.5 or more in the case where a gray scale (produced by
Kodak Japan Ltd.) was scanned by a scanner (CANOSCAN 4400, produced
by Canon Inc.), the obtained digital gray-scale values were
correlated with density values measured by a reflection
densitometer (RD-914, produced by Macbeth Co.), and the digital
gray-scale values, obtained by scanning a recorded image with the
scanner, were converted to the density values; and the line width
was calculated from a predetermined number of pixels (1,200 dpi)
for the digital gray-scale values. Thus, the line width was 0.45
mm.
[0303] Next, the laser output, the irradiation distance, the spot
diameter and the scanning speed were adjusted to 20 W, 195 mm, 3 mm
and 1,000 mm/s, respectively, and a laser beam was linearly scanned
across the recorded image at intervals of 0.59 mm so as to erase
the image. The density of the erased portion at that time was
0.15.
[0304] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 50 times, it turned out that image
erasure was possible with a density of 0.17 at the time when
repeated 700 times, and that an unerased portion was left with a
density of 0.20 at the time when repeated 750 times.
[0305] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.29 mm. The results are shown in Table 1.
Example 8
[0306] A semiconductor laser device equipped with a fiber coupled
semiconductor laser having an output of 25 W and an emission
wavelength of 808 nm, in which an aspheric element lens was
incorporated in the optical path, was used as a light source of a
semiconductor laser as shown in FIG. 3, and an image was recorded
onto the thermoreversible recording medium of Production Example 1
by applying a laser beam, as the laser output, the irradiation
distance, the focal distance of the f.theta. lens, the spot
diameter and the scanning speed were adjusted to 14.0 W, 154 mm,
150 mm, 0.91 mm and 1,000 mm/s, respectively. On this occasion, the
irradiation intensity (I.sub.1) of the applied laser beam in a
central position of the applied laser beam was 1.24 times the
irradiation intensity (I.sub.2) of the applied laser beam on a
plane corresponding to 95% of the total irradiation energy of the
applied laser beam. The line width was 0.44 mm.
[0307] Next, the laser output, the irradiation distance, the spot
diameter and the scanning speed were adjusted to 20 W, 195 mm, 3 mm
and 1,000 mm/s, respectively, and a laser beam was linearly scanned
across the recorded image at intervals of 0.59 mm so as to erase
the image. The density of the erased portion at that time was
0.15.
[0308] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 50 times, it turned out that image
erasure was possible with a density of 0.17 at the time when
repeated 700 times, and that an unerased portion was left with a
density of 0.20 at the time when repeated 750 times.
[0309] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.29 mm. The results are shown in Table 1.
Example 9
[0310] When recording and erasure were repeatedly carried out under
the conditions of Example 1 without cooling the light source of the
semiconductor laser, the temperature of the semiconductor laser was
raised to 40.degree. C. and blurring in a line occurred.
Example 10
[0311] The following image forming step and image erasing step were
carried out on the thermoreversible recording medium of Production
Example 1.
<Image Forming Step>
[0312] A 140 W fiber-coupled high-output semiconductor laser device
equipped with a light collecting optical system f100 (NBITS140mkII,
center wavelength: 808 nm, core diameter of an optical fiber: 600
.mu.m, NA: 0.22, produced by Jenoptik) was used as a laser, and the
laser output, the irradiation distance and the spot diameter were
adjusted to 12 W, 91.7 mm and approximately 0.6 mm, respectively. A
linear image was formed on the thermoreversible recording medium by
applying a laser beam at a feed speed of XY stage of 1,200 mm/s. On
this occasion, the irradiation intensity (I.sub.1) of the applied
laser beam in a central position of the applied laser beam was 1.25
times the irradiation intensity (I.sub.2) of the applied laser beam
on a plane corresponding to 95% of the total irradiation energy of
the applied laser beam.
<Image Erasing Step>
[0313] Next, the image was erased by heating the image at
140.degree. C. for 1 sec under a pressure of 1 kgf/cm.sup.2, using
a thermal inclination tester (TYPE HG-100, produced by Toyo Seiki
Co., Ltd.).
[0314] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 10 times, it turned out that image
erasure was possible with a density of 0.17 at the time when
repeated 90 times, and that an unerased portion was left with a
density of 0.20 at the time when repeated 100 times.
[0315] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.25 mm. The results are shown in Table 1.
Example 11
[0316] The same semiconductor laser device as the one in Example 1
was used, the thermoreversible recording medium of Production
Example 1 was affixed to a plastic box, and all the letters ("A" to
"Z") in the English alphabet were recorded, under the recording
conditions of Example 1, onto the thermoreversible recording medium
while being moved at a conveyance speed of 3 m/min on a conveyor
belt.
[0317] Next, all the letters ("A" to "Z") in the English alphabet
were erased, under the erasure conditions of Example 1, from the
thermoreversible recording medium affixed to the plastic box, while
being moved at a conveyance speed of 3 m/min on the conveyor
belt.
Comparative Example 1
[0318] The same semiconductor laser device as the one in Example 1
was used, and an image was recorded onto the thermoreversible
recording medium of Production Example 1 by applying a laser beam,
as the laser output, the irradiation distance, the spot diameter
and the scanning speed were adjusted to 9.4 W, 160 mm, 0.75 mm and
1,000 mm/s, respectively. The irradiation intensity (II) of the
applied laser beam in a central position of the applied laser beam
was 1.43 times the irradiation intensity (12) of the applied laser
beam on a plane corresponding to 95% of the total irradiation
energy of the applied laser beam. The irradiation intensity
distribution of the applied laser beam is substantially the same as
a Gaussian distribution. The line width, which was measured
similarly to that in Example 1, was 0.33 mm.
[0319] Next, the laser output, the irradiation distance, the spot
diameter and the scanning speed were adjusted to 20 W, 195 mm, 3 mm
and 1,000 mm/s, respectively, and a laser beam was linearly scanned
across the recorded image at intervals of 0.59 mm so as to erase
the image. The density of the erased portion at that time was
0.15.
[0320] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 10 times, it turned out that image
erasure was possible with a density of 0.17 at the time when
repeated 40 times, and that an unerased portion was left with a
density of 0.24 at the time when repeated 50 times.
[0321] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.17 mm. The results are shown in Table 1.
Comparative Example 2
[0322] The same semiconductor laser device as the one in Example 1
was used, and an image was recorded onto the thermoreversible
recording medium of Production Example 1 by applying a laser beam,
as the laser output, the irradiation distance, the spot diameter
and the scanning speed were adjusted to 9.3 W, 156 mm, 0.73 mm and
1,000 mm/s, respectively. The irradiation intensity (I.sub.1) of
the applied laser beam in a central position of the applied laser
beam was 1.30 times the irradiation intensity (I.sub.2) of the
applied laser beam on a plane corresponding to 95% of the total
irradiation energy of the applied laser beam. The line width, which
was measured similarly to that in Example 1, was 0.33 mm.
[0323] Next, the laser output, the irradiation distance, the spot
diameter and the scanning speed were adjusted to 20 W, 195 mm, 3 mm
and 1,000 mm/s, respectively, and a laser beam was linearly scanned
across the recorded image at intervals of 0.59 mm so as to erase
the image. The density of the erased portion at that time was
0.15.
[0324] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 10 times, it turned out that image
erasure was possible with a density of 0.17 at the time when
repeated 100 times, and that an unerased portion was left with a
density of 0.20 at the time when repeated 110 times.
[0325] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.19 mm. The results are shown in Table 1.
Comparative Example 3
[0326] The same semiconductor laser device as the one in Example 1
was used, and an image was recorded onto the thermoreversible
recording medium of Production Example 1 by applying a laser beam,
as the laser output, the irradiation distance, the spot diameter
and the scanning speed were adjusted to 9.1 W, 148 mm, 0.73 mm and
1,000 mm/s, respectively. The irradiation intensity (I.sub.1) of
the applied laser beam in a central position of the applied laser
beam was 1.19 times the irradiation intensity (I.sub.2) of the
applied laser beam on a plane corresponding to 95% of the total
irradiation energy of the applied laser beam. The line width, which
was measured similarly to that in Example 1, was 0.33 mm.
[0327] Next, the laser output, the irradiation distance, the spot
diameter and the scanning speed were adjusted to 20 W, 195 mm, 3 mm
and 1,000 mm/s, respectively, and a laser beam was linearly scanned
across the recorded image at intervals of 0.59 mm so as to erase
the image. The density of the erased portion at that time was
0.15.
[0328] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 50 times, it turned out that image
erasure was possible with a density of 0.17 at the time when
repeated 800 times, and that an unerased portion was left with a
density of 0.20 at the time when repeated 850 times.
[0329] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.30 mm. The results are shown in Table 1.
Comparative Example 4
[0330] Image recording and image erasure were carried out similarly
to those in Comparative Example 1, except that the thermoreversible
recording medium of Production Example 1 was changed to the
thermoreversible recording medium of Production Example 2, the
laser output at the time of image recording was changed to 6.6 W.
The irradiation intensity (I.sub.1) of the applied laser beam in a
central position of the applied laser beam was 1.43 times the
irradiation intensity (I.sub.2) of the applied laser beam on a
plane corresponding to 95% of the total irradiation energy of the
applied laser beam. The line width, which was measured similarly to
that in Example 4, was 0.33 mm.
[0331] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 10 times, it turned out that image
erasure was possible with a density of 1.64 at the time when
repeated 60 times, and that an unerased portion was left with a
density of 1.48 at the time when repeated 70 times.
[0332] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0. 18 mm. The results are shown in Table 1.
Comparative Example 5
[0333] Image recording and image erasure were carried out similarly
to those in Comparative Example 2, except that the thermoreversible
recording medium of Production Example 1 was changed to the
thermoreversible recording medium of Production Example 2, the
laser output at the time of image recording was changed to 6.5 W.
The irradiation intensity (I.sub.1) of the applied laser beam in a
central position of the applied laser beam was 1.30 times the
irradiation intensity (I.sub.2) of the applied laser beam on a
plane corresponding to 95% of the total irradiation energy of the
applied laser beam. The line width, which was measured similarly to
that in Example 4, was 0.33 mm.
[0334] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 10 times, it turned out that image
erasure was possible with a density of 1.64 at the time when
repeated 150 times, and that an unerased portion was left with a
density of 1.49 at the time when repeated 160 times.
[0335] Subsequently,, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.19 mm. The results are shown in Table 1.
Comparative Example 6
[0336] Image recording and image erasure were carried out similarly
to those in Comparative Example 3, except that the thermoreversible
recording medium of Production Example 1 was changed to the
thermoreversible recording medium of Production Example 2, the
laser output at the time of image recording was changed to 6.2 W.
The irradiation intensity (I.sub.1) of the applied laser beam in a
central position of the applied laser beam was 1.19 times the
irradiation intensity (I.sub.2) of the applied laser beam on a
plane corresponding to 95% of the total irradiation energy of the
applied laser beam. The line width, which was measured similarly to
that in Example 4, was 0.33 mm.
[0337] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 100 times, it turned out that image
erasure was possible with a density of 1.63 at the time when
repeated 1,300 times, and that an unerased portion was left with a
density of 1.57 at the time when repeated 1,400 times.
[0338] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.31 mm. The results are shown in Table 1.
Comparative Example 7
[0339] The same semiconductor laser device as the one in Example 1
was used, the thermoreversible recording medium of Production
Example 1 was affixed to a plastic box, and all the letters ("A" to
"Z") in the English alphabet were recorded, under the recording
conditions of Comparative Example 1, onto the thermoreversible
recording medium while being moved at a conveyance speed of 5 m/min
on a conveyor belt.
[0340] Next, all the letters ("A" to "Z") in the English alphabet
were erased, under the erasure conditions of Comparative Example 1,
from the thermoreversible recording medium affixed to the plastic
box, while being moved at a conveyance speed of 5 m/min on the
conveyor belt.
[0341] When image recording and image erasure were repeated under
the above-mentioned conditions, an unerased portion was left at the
time when repeated 50 times as in Comparative Example 1.
Comparative Example 8
[0342] The following image forming step and image erasing step were
carried out on the thermoreversible recording medium of Production
Example 1.
<Image Forming Step>
[0343] A 140 W fiber-coupled high-output semiconductor laser device
equipped with a light collecting optical system f100 (NBT-S140mkII,
center wavelength: 808 nm, core diameter of an optical fiber: 600
.mu.m, NA: 0.22, produced by Jenoptik) was used as a laser, and the
laser output, the irradiation distance and the spot diameter were
adjusted to 12 W, 92.0 mm and approximately 0.6 mm, respectively. A
linear image was formed on the thermoreversible recording medium by
applying a laser beam at a feed speed of XY stage of 1,200 mm/s. On
this occasion, the irradiation intensity (I.sub.1) of the applied
laser beam in a central position of the applied laser beam was 1.30
times the irradiation intensity (I.sub.2) of the applied laser beam
on a plane corresponding to 95% of the total irradiation energy of
the applied laser beam.
<Image Erasing Step>
[0344] Next, the image was erased by heating the image at
140.degree. C. for 1 sec under a pressure of 1 kgf/cm.sup.2, using
a thermal inclination tester (TYPE HG-100, produced by Toyo Seiki
Co., Ltd.). When image recording and image erasure were repeated
under the above-mentioned conditions, and the density of the erased
portion was measured once every 5 times, it turned out that image
erasure was possible with a density of 0.17 at the time when
repeated 30 times, and that an unerased portion was left with a
density of 0.20 at the time when repeated 35 times.
[0345] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.24 mm. The results are shown in Table 1.
Comparative Example 9
[0346] The following image forming step and image erasing step were
carried out on the thermoreversible recording medium of Production
Example 1.
<Image Forming Step>
[0347] A 140 W fiber-coupled high-output semiconductor laser device
equipped with a light collecting optical system f100 (NBT-S140mkII,
center wavelength: 808 nm, core diameter of an optical fiber: 600
.mu.m, NA: 0.22, produced by Jenoptik) was used as a laser, the
laser output, the irradiation distance and the spot diameter were
adjusted to 12 W, 91.4 mm and approximately 0.6 mm, respectively. A
linear image was formed on the thermoreversible recording medium by
applying a laser beam at a feed speed of XY stage of 1,200
mm/s.
[0348] On this occasion, the irradiation intensity (I.sub.1) of the
applied laser beam in a central position of the applied laser beam
was 1.19 times the irradiation intensity (I.sub.2) of the applied
laser beam on a plane corresponding to 95% of the total irradiation
energy of the applied laser beam.
<Image Erasing Step>
[0349] Next, the image was erased by heating the image at
140.degree. C. for 1 sec under a pressure of 1 kgf/cm.sup.2, using
a thermal inclination tester (TYPE HG-100, produced by Toyo Seiki
Co., Ltd.). When image recording and image erasure were repeated
under the above-mentioned conditions, and the density of the erased
portion was measured once every 10 times, it turned out that image
erasure was possible with a density of 0.17 at the time when
repeated 100 times, and that an unerased portion was left with a
density of 0.20 at the time when repeated 110 times.
[0350] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.37 mm. The results are shown in Table 1.
Comparative Example 10
[0351] The following image forming step and image erasing step were
carried out on the thermoreversible recording medium of Production
Example 1.
<Image Forming Step>
[0352] A 140 W fiber-coupled high-output semiconductor laser device
equipped with a light collecting optical system f100 (NBT-S140mkII,
center wavelength: 808 nm, core diameter of an optical fiber: 600
.mu.m, NA: 0.22, produced by Jenoptik) was used as a laser, the
laser output, the irradiation distance and the spot diameter were
adjusted to 12 W, 92.5 mm and approximately 0.6 mm, respectively. A
linear image was formed on the thermoreversible recording medium by
applying a laser beam at a feed speed of XY stage of 1,200
mm/s.
[0353] On this occasion, the irradiation intensity (I.sub.1) of the
applied laser beam in a central position of the applied laser beam
was 1.43 times the irradiation intensity (I.sub.2) of the applied
laser beam on a plane corresponding to 95% of the total irradiation
energy of the applied laser beam.
<Image Erasing Step>
[0354] Next, the image was erased by heating the image at
140.degree. C. for 1 sec under a pressure of 1 kgf/cm.sup.2, using
a thermal inclination tester (TYPE HG-100, produced by Toyo Seiki
Co., Ltd.).
[0355] When image recording and image erasure were repeated under
the above-mentioned conditions, and the density of the erased
portion was measured once every 2 times, it turned out that image
erasure was possible with a density of 0.17 at the time when
repeated 10 times, and that an unerased portion was left with a
density of 0.20 at the time when repeated 110 times.
[0356] Subsequently, when an image was recorded under the
above-mentioned recording conditions except that the laser output
was reduced, the minimum width of the line free from blurring was
0.18 mm. The results are shown in Table 1.
TABLE-US-00001 TABLE 1 Line width free Durability Printed from
blurring upon against line reduction of the I.sub.1/I.sub.2
repeated use width laser output Example 1 1.29 250 times 0.33 mm
0.20 mm Example 2 1.25 400 times 0.33 mm 0.21 mm Example 3 1.20 600
times 0.33 mm 0.25 mm Example 4 1.29 400 times 0.33 mm 0.21 mm
Example 5 1.25 600 times 0.33 mm 0.22 mm Example 6 1.20 800 times
0.33 mm 0.25 mm Example 7 1.25 700 times 0.45 mm 0.29 mm Example 8
1.24 700 times 0.44 mm 0.29 mm Comparative 1.43 40 times 0.33 mm
0.17 mm Example 1 Comparative 1.30 100 times 0.33 mm 0.19 mm
Example 2 Comparative 1.19 800 times 0.33 mm 0.30 mm Example 3
Comparative 1.43 60 times 0.33 mm 0.18 mm Example 4 Comparative
1.30 150 times 0.33 mm 0.19 mm Example 5 Comparative 1.19 1,300
times 0.33 mm 0.31 mm Example 6 Example 10 1.25 90 times 0.40 mm
0.25 mm Comparative 1.30 30 times 0.40 mm 0.24 mm Example 8
Comparative 1.19 100 times 0.40 mm 0.37 mm Example 9 Comparative
1.43 10 times 0.40 mm 0.17 mm Example 10 I.sub.1: irradiation
intensity of an applied laser beam in a central position of the
applied laser beam I.sub.2: irradiation intensity of an applied
laser beam on a plane corresponding to 95% of the total irradiation
energy of the applied laser beam
[0357] The image processing method and the image processing
apparatus of the present invention are capable of repeatedly
recording and erasing a high-contrast image at high speed and in a
noncontact manner onto and from a thermoreversible recording
medium, for example a label affixed to cardboard or to a receptacle
such as a plastic container, and also capable of reducing
degradation of the thermoreversible recording medium caused by
repeated use, and thus being particularly suitably used in product
distribution and delivery systems.
* * * * *